skip to main content


Title: The seed‐specific heat shock factor A9 regulates the depth of dormancy in Medicago truncatula seeds via ABA signalling
Abstract

During the later stages of seed maturation, two key adaptive traits are acquired that contribute to seed lifespan and dispersal, longevity and dormancy. The seed‐specific heat shock transcription factor A9 is an important hub gene in the transcriptional network of late seed maturation. Here, we demonstrate that HSFA9 plays a role in thermotolerance rather than in ex situ seed conservation. Storage ofhsfa9seeds ofMedicago truncatulaand Arabidopsis had comparable lifespan at moderate storage relative humidity (RH), whereas at high RH,hsfa9seeds lost their viability much faster than wild type seeds. Furthermore, we show that inM.truncatula, Mthsfa9seeds acquired more dormancy during late maturation than wild type. Transient expression of MtHSFA9in hairy roots and transcriptome analysis of Mthsfa9Tnt1 insertion mutants identified a deregulation of genes involved in ABA biosynthesis, catabolism and signalling. Consistent with these results,Mthsfa9seeds exhibited increased ABA levels and higher sensitivity to ABA. These data suggest that in legumes,HSFA9acts as a negative regulator of the depth of seed dormancy during seed development via the modulation of hormonal balance.

 
more » « less
NSF-PAR ID:
10185996
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley-Blackwell
Date Published:
Journal Name:
Plant, Cell & Environment
Volume:
43
Issue:
10
ISSN:
0140-7791
Page Range / eLocation ID:
p. 2508-2522
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. SUMMARY

    Arabidopsis thalianaABSCISIC ACID INSENSITIVE3 (ABI3) is a transcription factor in the B3 domain family. ABI3, along with B3 domain transcription factors LEAFY COTYLEDON2 (LEC2) and FUSCA3 (FUS3), and LEC1, a subunit of the CCAAT box‐binding complex, form the so‐called LAFL network to control various aspects of seed development and maturation. ABI3 also contributes to the abscisic acid (ABA) response. We report on chromatin immunoprecipitation‐tiling array experiments to map binding sites for ABI3 globally. We also assessed transcriptomes in response to ABI3 by comparing developingabi3‐5and wild‐type seeds and combined this information to ascertain direct and indirect responsive ABI3 target genes. ABI3 can induce and repress its transcription of target genes directly and some intriguing differences exist incismotifs between these groups of genes. Directly regulated targets reflect the role of ABI3 in seed maturation, desiccation tolerance, entry into a quiescent state and longevity. Interestingly, ABI3 directly represses a gene encoding a microRNA (MIR160B) that targetsAUXIN RESPONSE FACTOR(ARF)10andARF16that are involved in establishment of dormancy. In addition, ABI3, like FUS3, regulates genes encodingMIR156but while FUS3 only induces genes encoding this product, ABI3 induces these genes during the early stages of seed development, but represses these genes during late development. The interplay between ABI3, the otherLAFLgenes, and theVP1/ABI3‐LIKE(VAL) genes, which are involved in the transition to seedling development are examined and reveal complex interactions controlling development.

     
    more » « less
  2. SUMMARY

    Flowering of the reference legumeMedicago truncatulais promoted by winter cold (vernalization) followed by long‐day photoperiods (VLD) similar to winter annual Arabidopsis. However, Medicago lacksFLCandCO, key regulators of Arabidopsis VLD flowering.Most plants have twoINHIBITOR OF GROWTH(ING) genes (ING1andING2), encoding proteins with an ING domain with two anti‐parallel alpha‐helices and a plant homeodomain (PHD) finger, but their genetic role has not been previously described.In Medicago,Mting1gene‐edited mutants developed and flowered normally, but anMting2‐1 Tnt1insertion mutant and gene‐editedMting2mutants had developmental abnormalities including delayed flowering particularly in VLD, compact architecture, abnormal leaves with extra leaflets but no trichomes, and smaller seeds and barrels.Mting2mutants had reduced expression of activators of flowering, including theFT‐like geneMtFTa1, and increased expression of the candidate repressorMtTFL1c, consistent with the delayed flowering of the mutant.MtING2overexpression complementedMting2‐1, but did not accelerate flowering in wild type. The MtING2 PHD finger bound H3K4me2/3 peptides weaklyin vitro, but analysis of gene‐edited mutants indicated that it was dispensable to MtING2 function in wild‐type plants. RNA sequencing experiments indicated that >7000 genes are mis‐expressed in theMting2‐1mutant, consistent with its strong mutant phenotypes. Interestingly, ChIP‐seq analysis identified >5000 novel H3K4me3 locations in the genome ofMting2‐1mutants compared to wild type R108. Overall, our mutant study has uncovered an important physiological role of a plantING2gene in development, flowering, and gene expression, which likely involves an epigenetic mechanism.

     
    more » « less
  3. Abstract

    Pioneer trees require high‐light environments for successful seedling establishment. Consequently, seeds of these species often persist in the soil seed bank (SSB) for periods ranging from several weeks to decades. How they survive despite extensive pressure from seed predators and soil‐borne pathogens remains an intriguing question.

    This study aims to test the hypotheses that decades‐old seeds collected from the SSB in a lowland tropical forest remain viable by (i) escaping infection by fungi, which are major drivers of seed mortality in tropical soils, and/or (ii) maintaining high levels of seed dormancy and seed coat integrity when compared to inviable seeds.

    We collected seeds ofTrema micranthaandZanthoxylum ekmaniiat Barro Colorado Island, Panama, from sites where adult trees previously occurred in the past 30 years. We used carbon dating to measure seed age and characterized seed coat integrity, seed dormancy and fungal communities.

    Viable seeds from the SSB ranged in age from 9 to 30 years forT. micrantha, and 5 to 33 years forZ. ekmanii. We found no evidence that decades‐old seeds maintain high levels of seed dormancy or seed coat integrity. Fungi were rarely detected in fresh seeds (no soil contact), but phylogenetically diverse fungi were detected often in seeds from the SSB. Although fungal infections were more commonly detected in inviable seeds than in viable seeds, a lack of differences in fungal diversity and community composition between viable and inviable seeds suggested that viable seeds are not simply excluding fungal species to survive long periods in the SSB.

    Synthesis.Our findings reveal the importance of a previously understudied aspect of seed survival, where the impact of seed–microbial interactions may be critical to understand long‐term persistence in the SSB.

    Read the freePlain Language Summaryfor this article on the Journal blog.

     
    more » « less
  4. Summary

    Despite well established roles of microRNAs in plant development, few aspects have been addressed to understand their effects in seeds especially on lipid metabolism. In this study, we showed that overexpressing microRNA167A (miR167OE) in camelina (Camelina sativa) under a seed‐specific promoter changed fatty acid composition and increased seed size. Specifically, the miR167OEseeds had a lower α‐linolenic acid with a concomitantly higher linoleic acid content than the wild‐type. This decreased level of fatty acid desaturation corresponded to a decreased transcriptional expression of the camelina fatty acid desaturase3 (CsFAD3) in developing seeds. MiR167 targeted the transcription factor auxin response factor (CsARF8) in camelina, as had been reported previously in Arabidopsis. Chromatin immunoprecipitation experiments combined with transcriptome analysis indicated that CsARF8 bound to promoters of camelinabZIP67andABI3genes. These transcription factors directly or through theABI3‐bZIP12 pathway regulateCsFAD3expression and affect α‐linolenic acid accumulation. In addition, to decipher the miR167A‐CsARF8 mediated transcriptional cascade forCsFAD3suppression, transcriptome analysis was conducted to implicate mechanisms that regulate seed size in camelina. Expression levels of many genes were altered in miR167OE, including orthologs that have previously been identified to affect seed size in other plants. Most notably, genes for seed coat development such as suberin and lignin biosynthesis were down‐regulated. This study provides valuable insights into the regulatory mechanism of fatty acid metabolism and seed size determination, and suggests possible approaches to improve these important traits in camelina.

     
    more » « less
  5. Summary

    Arbuscular mycorrhizal fungi help their host plant in the acquisition of nutrients, and this association is itself impacted by soil nutrient levels. High phosphorus levels inhibit the symbiosis, whereas high nitrogen levels enhance it. The genetic mechanisms regulating the symbiosis in response to soil nutrients are poorly understood. Here, we characterised the symbiotic phenotypes in fourMedicago truncatula Tnt1‐insertion mutants affected in arbuscular mycorrhizal colonisation. We located theirTnt1insertions and identified alleles for two genes known to be involved in mycorrhization,RAM1andKIN3. We compared the effects of thekin3‐2andram1‐4mutations on gene expression, revealing that the two genes alter the expression of overlapping but not identical gene sets, suggesting thatRAM1acts upstream ofKIN3.Additionally,KIN3appears to be involved in the suppression of plant defences in response to the fungal symbiont.KIN3is located on the endoplasmic reticulum of arbuscule‐containing cortical cells, andkin3‐2mutants plants hosted significantly fewer arbuscules than the wild type.KIN3plays an essential role in the symbiotic response to soil nitrogen levels, as, contrary to wild‐type plants, thekin3‐2mutant did not exhibit increased root colonisation under high nitrogen.

     
    more » « less