Mol Plant , IF:12.084 , 2021 Apr , V14 (4) : P588-603 doi: 10.1016/j.molp.2021.01.019
Dynamic spatial reorganization of BSK1 complexes in the plasma membrane underpins signal-specific activation for growth and immunity.
Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China; College of Biological Sciences & Biotechnology, Beijing Forestry University, Beijing 100083, China.; College of Biological Sciences & Biotechnology, Beijing Forestry University, Beijing 100083, China.; Institute of Cellular and Molecular Botany, University of Bonn, Bonn, 53115, Germany.; College of Biological Sciences & Biotechnology, Beijing Forestry University, Beijing 100083, China; Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, 37673, Korea.; College of Biological Sciences & Biotechnology, Beijing Forestry University, Beijing 100083, China. Electronic address: shanxy80@tsinghua.edu.cn.; Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China; College of Biological Sciences & Biotechnology, Beijing Forestry University, Beijing 100083, China. Electronic address: linjx@ibcas.ac.cn.
Growth and immunity are opposing processes that compete for cellular resources, and proper resource allocation is crucial for plant survival. BSK1 plays a key role in the regulation of both growth and immunity by associating with BRI1 and FLS2, respectively. However, it remains unclear how two antagonistic signals co-opt BSK1 to induce signal-specific activation. Here we show that the dynamic spatial reorganization of BSK1 within the plasma membrane underlies the mechanism of signal-specific activation for growth or immunity. Resting BSK1 localizes to membrane rafts as complexes. Unlike BSK1-associated FLS2 and BRI1, flg22 or exogenous brassinosteroid (BR) treatment did not decrease BSK1 levels at the plasma membrane (PM) but rather induced BSK1 multimerization and dissociation from FLS2/BSK1 or BRI1/BSK1, respectively. Moreover, flg22-activated BSK1 translocated from membrane rafts to non-membrane-raft regions, whereas BR-activated BSK1 remained in membrane rafts. When applied together with flg22, BR suppressed various flg22-induced BSK1 activities such as BSK1 dissociation from FLS2/BSK1, BSK1 interaction with MAPKKK5, and BSK translocation together with MAPKKK5. Taken together, this study provides a unique insight into how the precise control of BSK1 spatiotemporal organization regulates the signaling specificity to balance plant growth and immunity.
PMID: 33524551
Plant Cell , IF:9.618 , 2021 Apr doi: 10.1093/plcell/koab112
Arabidopsis NF-YCs play dual roles in repressing brassinosteroid biosynthesis and signaling during light-regulated hypocotyl elongation.
Key Laboratory of South China Agricultural Plant Molecular Analysis and Genetic Improvement & Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Innovative Academy of Seed Design, Chinese Academy of Sciences, Guangzhou, China.; University of the Chinese Academy of Sciences, Beijing, China.; School of Life Sciences, Guangzhou University, Guangzhou, China.
Light functions as the primary environmental stimulus and brassinosteroids (BRs) as important endogenous growth regulators throughout the plant lifecycle. Photomorphogenesis involves a series of vital developmental processes that require the suppression of BR-mediated seedling growth, but the mechanism underlying the light-controlled regulation of the BR pathway remain unclear. Here, we reveal that nuclear factor YC proteins (NF-YCs) function as essential repressors of the BR pathway during light-controlled hypocotyl growth in Arabidopsis thaliana. In the light, NF-YCs inhibit BR biosynthesis by directly targeting the promoter of the BR biosynthesis gene BR6ox2 and repressing its transcription. NF-YCs also interact with BIN2, a critical repressor of BR signaling, and facilitate its stabilization by promoting its Tyr200 autophosphorylation, thus inhibiting the BR signaling pathway. Consistently, loss-of-function mutants of NF-YCs show etiolated growth and constitutive BR responses, even in the light. Our findings uncover a dual role of NF-YCs in repressing BR biosynthesis and signaling, providing mechanistic insights into how light antagonizes the BR pathway to ensure photomorphogenic growth in Arabidopsis.
PMID: 33871651
New Phytol , IF:8.512 , 2021 Apr doi: 10.1111/nph.17403
BRASSINOSTEROID-SIGNALING KINASE 1 phosphorylating CALCIUM/CALMODULIN-DEPENDENT PROTEIN KINASE functions in drought tolerance in maize.
College of Life Sciences, Nanjing Agricultural University, Nanjing, 210095, China.; Institute of Food Crops, Provincial Key Laboratory of Agrobiology, Jiangsu Academy of Agricultural Sciences, Nanjing, 210014, China.; National Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing, 210095, China.
Drought stress seriously limits crop productivity. Although studies have been carried out, it is still largely unknown that how plant responds to drought stress. Here we find that drought treatment can enhance the phosphorylation activity of brassinosteroid-signaling kinase 1 (ZmBSK1) in maize (Zea mays). Our genetic studies reveal that ZmBSK1 positively affects drought tolerance in maize plants. ZmBSK1 localizes in plasma membrane, interacts with calcium/calmodulin-dependent protein kinase (ZmCCaMK), and phosphorylates ZmCCaMK. Ser-67 is a crucial phosphorylation site of ZmCCaMK by ZmBSK1. Drought stress enhances not only the interaction between ZmBSK1 and ZmCCaMK but also the phosphorylation of Ser-67 in ZmCCaMK by ZmBSK1. Furthermore, Ser-67 phosphorylation in ZmCCaMK regulates its Ca(2+) /CaM binding, autophosphorylation activity and transphosphorylation activity, and positively affects its function in drought tolerance in maize. Our results reveal an important role of ZmBSK1 in drought tolerance and suggest a direct regulatory mode of ZmBSK1 phosphorylating ZmCCaMK.
PMID: 33864702
New Phytol , IF:8.512 , 2021 Apr , V230 (1) : P228-243 doi: 10.1111/nph.17144
Modulation of Arabidopsis root growth by specialized triterpenes.
Department of Plant Biotechnology and Bioinformatics, Ghent University, Technologiepark 71, Ghent, 9052, Belgium.; VIB Center for Plant Systems Biology, Technologiepark 71, Ghent, 9052, Belgium.; Department of Metabolic Biology, John Innes Centre, Norwich Research Park, Colney Lane, Norwich,, NR4 7UH, UK.; Laboratory of Molecular Cell Biology, KU Leuven, Kasteelpark Arenberg 31, Leuven, 3000, Belgium.; VIB Center for Microbiology, Kasteelpark Arenberg 31, Leuven, 3000, Belgium.; Department of Organic Chemistry, Institute of Chemistry, Sao Paulo State University (UNESP), Araraquara, Sao Paulo, 14800-060, Brazil.; Laboratory of Growth Regulators, Institute of Experimental Botany of the Czech Academy of Sciences and Faculty of Science of Palacky University, Slechtitelu 27, Olomouc, CZ-78371, Czech Republic.; Department of Organic Chemistry, Ghent University, Ghent, 9000, Belgium.; Department of Forest Genetics and Plant Physiology, Umea Plant Science Centre, Swedish University of Agricultural Sciences, Umea, SE-901 83, Sweden.; Lab of Plant Growth Analysis, Ghent University Global Campus, Incheon, 21985, Korea.
Plant roots are specialized belowground organs that spatiotemporally shape their development in function of varying soil conditions. This root plasticity relies on intricate molecular networks driven by phytohormones, such as auxin and jasmonate (JA). Loss-of-function of the NOVEL INTERACTOR OF JAZ (NINJA), a core component of the JA signaling pathway, leads to enhanced triterpene biosynthesis, in particular of the thalianol gene cluster, in Arabidopsis thaliana roots. We have investigated the biological role of thalianol and its derivatives by focusing on Thalianol Synthase (THAS) and Thalianol Acyltransferase 2 (THAA2), two thalianol cluster genes that are upregulated in the roots of ninja mutant plants. THAS and THAA2 activity was investigated in yeast, and metabolite and phenotype profiling of thas and thaa2 loss-of-function plants was carried out. THAA2 was shown to be responsible for the acetylation of thalianol and its derivatives, both in yeast and in planta. In addition, THAS and THAA2 activity was shown to modulate root development. Our results indicate that the thalianol pathway is not only controlled by phytohormonal cues, but also may modulate phytohormonal action itself, thereby affecting root development and interaction with the environment.
PMID: 33616937
New Phytol , IF:8.512 , 2021 Apr , V230 (2) : P475-484 doi: 10.1111/nph.17198
The geometry of the compound leaf plays a significant role in the leaf movement of Medicago truncatula modulated by mtdwarf4a.
CAS Key Laboratory of Tropical Plant Resources and Sustainable Use, CAS Center for Excellence in Molecular Plant Sciences, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, 88 Xuefu Road, Kunming, Yunnan, 650223, China.; University of Chinese Academy of Sciences, Beijing, 100049, China.; School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, 230027, China.; Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, China.; Department of Plant and Soil Sciences, Institute for Agricultural Biosciences, Oklahoma State University, 3210 Sam Noble Parkway, Ardmore, OK, 73401, USA.
In most legumes, two typical features found in leaves are diverse compound forms and the pulvinus-driven nyctinastic movement. Many genes have been identified for leaf-shape determination, but the underlying nature of leaf movement as well as its association with the compound form remains largely unknown. Using forward-genetic screening and whole-genome resequencing, we found that two allelic mutants of Medicago truncatula with unclosed leaflets at night were impaired in MtDWARF4A (MtDWF4A), a gene encoding a cytochrome P450 protein orthologous to Arabidopsis DWARF4. The mtdwf4a mutant also had a mild brassinosteroid (BR)-deficient phenotype bearing pulvini without significant deficiency in organ identity. Both mtdwf4a and dwf4 could be fully rescued by MtDWF4A, and mtdwf4a could close their leaflets at night after the application of exogenous 24-epi-BL. Surgical experiments and genetic analysis of double mutants revealed that the failure to exhibit leaf movement in mtdwf4a is a consequence of the physical obstruction of the overlapping leaflet laminae, suggesting a proper geometry of leaflets is important for their movement in M. truncatula. These observations provide a novel insight into the nyctinastic movement of compound leaves, shedding light on the importance of open space for organ movements in plants.
PMID: 33458826
Plant Biotechnol J , IF:8.154 , 2021 Apr , V19 (4) : P702-716 doi: 10.1111/pbi.13496
Overexpression of GmMYB14 improves high-density yield and drought tolerance of soybean through regulating plant architecture mediated by the brassinosteroid pathway.
Key Laboratory of Biology and Genetic Improvement of Oil Crops, Ministry of Agriculture and Rural Affairs, Oil Crops Research Institute, Chinese Academy of Agricultural Sciences, Wuhan, China.; The Industrial Crop Institute, Shanxi Academy of Agricultural Sciences, Taiyuan, China.; Institute of Genomics for Crop Abiotic Stress Tolerance, Department of Plant and Soil Science, Texas Tech University, Lubbock, TX, USA.; Stress Adaptation Research Unit, RIKEN Center for Sustainable Resource Science, Tsurumi, Yokohama, Japan.
MYB transcription factors (TFs) have been reported to regulate the biosynthesis of secondary metabolites, as well as to mediate plant adaption to abiotic stresses, including drought. However, the roles of MYB TFs in regulating plant architecture and yield potential remain poorly understood. Here, we studied the roles of the dehydration-inducible GmMYB14 gene in regulating plant architecture, high-density yield and drought tolerance through the brassinosteroid (BR) pathway in soybean. GmMYB14 was shown to localize to nucleus and has a transactivation activity. Stable GmMYB14-overexpressing (GmMYB14-OX) transgenic soybean plants displayed a semi-dwarfism and compact plant architecture associated with decreased cell size, resulting in a decrease in plant height, internode length, leaf area, leaf petiole length and leaf petiole angle, and improved yield in high density under field conditions. Results of the transcriptome sequencing suggested the involvement of BRs in regulating GmMYB14-OX plant architecture. Indeed, GmMYB14-OX plants showed reduced endogenous BR contents, while exogenous application of brassinolide could partly rescue the phenotype of GmMYB14-OX plants. Furthermore, GmMYB14 was shown to directly bind to the promoter of GmBEN1 and up-regulate its expression, leading to reduced BR content in GmMYB14-OX plants. GmMYB14-OX plants also displayed improved drought tolerance under field conditions. GmBEN1 expression was also up-regulated in the leaves of GmMYB14-OX plants under polyethylene glycol treatment, indicating that the GmBEN1-mediated reduction in BR level under stress also contributed to drought/osmotic stress tolerance of the transgenic plants. Our findings provided a strategy for stably increasing high-density yield and drought tolerance in soybean using a single TF-encoding gene.
PMID: 33098207
Plant Physiol , IF:6.902 , 2021 Apr , V185 (4) : P1745-1763 doi: 10.1093/plphys/kiab008
Brassinosteroid homeostasis is critical for the functionality of the Medicago truncatula pulvinus.
The Key Laboratory of Plant Development and Environmental Adaptation Biology, Ministry of Education, School of Life Sciences, Shandong University, Qingdao, 266237, China.; Shandong Provincial Key Laboratory of Plant Stress, Shandong Normal University, Jinan, 250013, China.; School of Life Sciences, Guangzhou University, Guangzhou, 510006, China.; Noble Research Institute, LLC, Ardmore, Oklahoma, 73401.; National Centre for Plant Gene Research (Beijing), Innovation Academy for Seed Design, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, 100101, China.; College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
Many plant species open their leaves during the daytime and close them at night as if sleeping. This leaf movement is known as nyctinasty, a unique and intriguing phenomenon that been of great interest to scientists for centuries. Nyctinastic leaf movement occurs widely in leguminous plants, and is generated by a specialized motor organ, the pulvinus. Although a key determinant of pulvinus development, PETIOLULE-LIKE PULVINUS (PLP), has been identified, the molecular genetic basis for pulvinus function is largely unknown. Here, through an analysis of knockout mutants in barrelclover (Medicago truncatula), we showed that neither altering brassinosteroid (BR) content nor blocking BR signal perception affected pulvinus determination. However, BR homeostasis did influence nyctinastic leaf movement. BR activity in the pulvinus is regulated by a BR-inactivating gene PHYB ACTIVATION TAGGED SUPPRESSOR1 (BAS1), which is directly activated by PLP. A comparative analysis between M. truncatula and the non-pulvinus forming species Arabidopsis and tomato (Solanum lycopersicum) revealed that PLP may act as a factor that associates with unknown regulators in pulvinus determination in M. truncatula. Apart from exposing the involvement of BR in the functionality of the pulvinus, these results have provided insights into whether gene functions among species are general or specialized.
PMID: 33793936
Plant Physiol , IF:6.902 , 2021 Apr , V185 (4) : P1903-1923 doi: 10.1093/plphys/kiaa116
A multifaceted module of BRI1 ETHYLMETHANE SULFONATE SUPRESSOR1 (BES1)-MYB88 in growth and stress tolerance of apple.
State Key Laboratory of Crop Stress Biology for Arid Areas/Shaanxi Key Laboratory of Apple, College of Horticulture, Northwest A&F University, Yangling, Shaanxi 712100, China.; State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi 712100, China.; College of Grassland Agriculture, Northwest A&F University, Yangling, Shaanxi 712100, China.
The R2R3 transcription factor MdMYB88 has previously been reported to function in biotic and abiotic stress responses. Here, we identify BRI1 ETHYLMETHANE SULFONATE SUPRESSOR1 (MdBES1), a vital component of brassinosteroid (BR) signaling in apple (Malus x domestica) that directly binds to the MdMYB88 promoter, regulating the expression of MdMYB88 in a dynamic and multifaceted mode. MdBES1 positively regulated expression of MdMYB88 under cold stress and pathogen attack, but negatively regulated its expression under control and drought conditions. Consistently, MdBES1 was a positive regulator for cold tolerance and disease resistance in apple, but a negative regulator for drought tolerance. In addition, MdMYB88 participated in BR biosynthesis by directly regulating the BR biosynthetic genes DE ETIOLATED 2 (MdDET2), DWARF 4 (MdDWF4), and BRASSINOSTEROID 6 OXIDASE 2 (MdBR6OX2). Applying exogenous BR partially rescued the erect leaf and dwarf phenotypes, as well as defects in stress tolerance in MdMYB88/124 RNAi plants. Moreover, knockdown of MdMYB88 in MdBES1 overexpression (OE) plants decreased resistance to a pathogen and C-REPEAT BINDING FACTOR1 expression, whereas overexpressing MdMYB88 in MdBES1 OE plants increased expression of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3 MdSPL3 and BR biosynthetic genes, suggesting that MdMYB88 contributes to MdBES1 function during BR biosynthesis and the stress response. Taken together, our results reveal multifaceted regulation of MdBES1 on MdMYB88 in BR biosynthesis and stress tolerance.
PMID: 33793930
Plant Physiol , IF:6.902 , 2021 Apr , V185 (4) : P1875-1893 doi: 10.1093/plphys/kiab013
The mechanism for brassinosteroids suppressing climacteric fruit ripening.
Key Laboratory of Fruit Postharvest Biology, Liaoning Province, College of Horticulture, Shenyang Agricultural University, Shenyang 110866, China.; National Centre for Plant Gene Research (Beijing), Innovation Academy for Seed Design, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.; College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing 100039, China.
The plant hormone ethylene is important for the ripening of climacteric fruit, such as pear (Pyrus ussuriensis), and the brassinosteroid (BR) class of phytohormones affects ethylene biosynthesis during ripening via an unknown molecular mechanism. Here, we observed that exogenous BR treatment suppressed ethylene production and delayed fruit ripening, whereas treatment with a BR biosynthesis inhibitor promoted ethylene production and accelerated fruit ripening in pear, suggesting BR is a ripening suppressor. The expression of the transcription factor BRASSINAZOLE-RESISTANT 1PuBZR1 was enhanced by BR treatment during pear fruit ripening. PuBZR1 interacted with PuACO1, which converts 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene, and suppressed its activity. BR-activated PuBZR1 bound to the promoters of PuACO1 and of PuACS1a, which encodes ACC synthase, and directly suppressed their transcription. Moreover, PuBZR1 suppressed the expression of transcription factor PuERF2 by binding its promoter, and PuERF2 bound to the promoters of PuACO1 and PuACS1a. We concluded that PuBZR1 indirectly suppresses the transcription of PuACO1 and PuACS1a through its regulation of PuERF2. Ethylene production and expression profiles of corresponding apple (Malus domestica) homologs showed similar changes following epibrassinolide treatment. Together, these results suggest that BR-activated BZR1 suppresses ACO1 activity and the expression of ACO1 and ACS1, thereby reducing ethylene production and suppressing fruit ripening. This likely represents a conserved mechanism by which BR suppresses ethylene biosynthesis during climacteric fruit ripening.
PMID: 33743010
Plant Cell Physiol , IF:4.062 , 2021 Apr doi: 10.1093/pcp/pcab051
Making the "Green Revolution" Truly Green: improving crop nitrogen use efficiency.
Bioscience and Biotechnology Center, Nagoya University, Nagoya, 464-8601, Japan.; Faculty of Food and Agricultural Sciences, Fukushima University, Fukushima 960-1248, Japan.
Traditional breeding for high-yielding crops has mainly relied on the widespread cultivation of gibberellin (GA)-deficient semi-dwarf varieties, as dwarfism increases lodging resistance and allows for high nitrogen use, resulting in high grain yield. Although the adoption of semi-dwarf varieties in rice and wheat breeding brought big success to the "Green Revolution" in the 20th century, it consequently increased the demand for nitrogen-based fertilizer, which causes severe threat to ecosystems and sustainable agriculture. In order to make the "Green Revolution" truly green, it is necessary to develop new varieties with high nitrogen-use efficiency (NUE). Under this demand, research on NUE, mainly for rice, has made great strides in the last decade. This mini-review focuses on three aspects of recent epoch-making findings on rice breeding for high NUE. The first one on "NUE genes related to GA signaling" shows how promising it is to improve NUE in semi-dwarf Green Revolution Varieties. The second aspect centers around the nitrate transporter1.1B, NRT1.1B; studies have revealed a nutrient signaling pathway through the discovery of the nitrate-NRT1.1B-SPX4-NLP3 cascade. The last one is based on the recent finding that the Teosinte branched1, Cycloidea, Proliferating cell factor (TCP)-domain protein 19 underlies the genomic basis of geographical adaptation to soil nitrogen; OsTCP19 regulates the expression of a key transacting factor, DLT/SMOS2, which participates in the signaling of four different phytohormones, GA, auxin, brassinosteroid and strigolactone. Collectively, these breakthrough findings represent a significant step towards breeding high NUE rice in the future.
PMID: 33836084
Plant Sci , IF:3.591 , 2021 Apr , V305 : P110846 doi: 10.1016/j.plantsci.2021.110846
The influence of ethylene, gibberellins and brassinosteroids on energy and nitrogen-fixation metabolites in nodule tissue.
School of Natural Sciences, University of Tasmania, Private Bag 55, Hobart, Tasmania, 7001, Australia.; School of Natural Sciences, University of Tasmania, Private Bag 55, Hobart, Tasmania, 7001, Australia. Electronic address: Eloise.foo@utas.edu.au.
Legume nodules are a unique plant organ that contain nitrogen-fixing rhizobial bacteria. For this interaction to be mutually beneficial, plant and bacterial metabolism must be precisely co-ordinated. Plant hormones are known to play essential roles during the establishment of legume-rhizobial symbioses but their role in subsequent nodule metabolism has not been explored in any depth. The plant hormones brassinosteroids, ethylene and gibberellins influence legume infection, nodule number and in some cases nodule function. In this paper, the influence of these hormones on nodule metabolism was examined in a series of well characterised pea mutants with altered hormone biosynthesis or response. A targeted set of metabolites involved in nutrient exchange and nitrogen fixation was examined in nodule tissue of mutant and wild type plants. Gibberellin-deficiency had a major negative impact on the level of several major dicarboxylates supplied to rhizobia by the plant and also led to a significant deficit in the amino acids involved in glutamine-aspartate transamination, consistent with the limited bacteroid development and low fixation rate of gibberellin-deficient na mutant nodules. In contrast, no major effects of brassinosteroid-deficiency or ethylene-insensitivity on the key metabolites in these pathways were found. Therefore, although all three hormones influence infection and nodule number, only gibberellin is important for the establishment of a functional nodule metabolome.
PMID: 33691972
Plant Mol Biol , IF:3.302 , 2021 Apr doi: 10.1007/s11103-021-01143-x
A coumarin exudation pathway mitigates arbuscular mycorrhizal incompatibility in Arabidopsis thaliana.
Plant-Microbe Interactions, Department of Biology, Science4Life, Utrecht University, PO Box 800.56, 3508 TB, Utrecht, the Netherlands. marco.rebecacosme@uclouvain.be.; Mycology, Applied Microbiology, Earth and Life Institute, Universite Catholique de Louvain, Croix du sud 2, bte L7.05.06, 1348, Louvain-la-Neuve, Belgium. marco.rebecacosme@uclouvain.be.; Plant-Microbe Interactions, Department of Biology, Science4Life, Utrecht University, PO Box 800.56, 3508 TB, Utrecht, the Netherlands.; Mycology, Applied Microbiology, Earth and Life Institute, Universite Catholique de Louvain, Croix du sud 2, bte L7.05.06, 1348, Louvain-la-Neuve, Belgium.; Plant-Soil Interactions, Department of Agroecology and Environment, Agroscope Reckenholz, Reckenholzstrasse 191, 8046, Zurich, Switzerland.; Department of Plant and Microbial Biology, University of Zurich, 8057, Zurich, Switzerland.
KEY MESSAGE: Overexpression of genes involved in coumarin production and secretion can mitigate mycorrhizal incompatibility in nonhost Arabidopsis plants. The coumarin scopoletin, in particular, stimulates pre-penetration development and metabolism in mycorrhizal fungi. Although most plants can benefit from mutualistic associations with arbuscular mycorrhizal (AM) fungi, nonhost plant species such as the model Arabidopsis thaliana have acquired incompatibility. The transcriptional response of Arabidopsis to colonization by host-supported AM fungi switches from initial AM recognition to defense activation and plant growth antagonism. However, detailed functional information on incompatibility in nonhost-AM fungus interactions is largely missing. We studied interactions between host-sustained AM fungal networks of Rhizophagus irregularis and 18 Arabidopsis genotypes affected in nonhost penetration resistance, coumarin production and secretion, and defense (salicylic acid, jasmonic acid, and ethylene) and growth hormones (auxin, brassinosteroid, cytokinin, and gibberellin). We demonstrated that root-secreted coumarins can mitigate incompatibility by stimulating fungal metabolism and promoting initial steps of AM colonization. Moreover, we provide evidence that major molecular defenses in Arabidopsis do not operate as primary mechanisms of AM incompatibility nor of growth antagonism. Our study reveals that, although incompatible, nonhost plants can harbor hidden tools that promote initial steps of AM colonization. Moreover, it uncovered the coumarin scopoletin as a novel signal in the pre-penetration dialogue, with possible implications for the chemical communication in plant-mycorrhizal fungi associations.
PMID: 33825084