The Function Of Arabidopsis NFTA1during Seed Germination

Seed germination is a critical process in the plant life cycle, which is determined by manyenvironmental factors, such as temperature, light, oxygen, water status and so on. Even afterthe break of dormancy, seeds fail to germinate and develop under unfavorable conditions.Abscisic acid (ABA) is an important phytohormone in regulating plant responses to a varietyof environmental stress, particularly water deprivation. It also plays a critical role inmediating the seed dormancy, seed germination and postgermination growth of the seeds,.The breaking of seed dormancy to enter normal seedling growth is a fragile phase that iseasily affected by environmental stresses, especially water deficit. Upon seed imbibition,ABA levels decrease to allow seeds to germinate and develop into seedlings. However, underabiotic stress conditions, ABA levels remain high, and the growth and development arearrested. Exposure of seeds to exogenous ABA during germination leads to rapid butreversible arrest in postgermination growth. However, the ABA-mediated growth arrest of thegerminated seeds represents a protective mechanism that helps these young seedlings surviveunder water deficit conditions.Nuclear factor Y (NF-Y) is a ubiquitous transcription factor in eukaryotes composed ofthree distinct subunits: NF-YA, NF-YB, and NF-YC. They can form a complex which has ahigh affinity and sequence specificity for the CCAAT box, a cis-element that exists in about25%of eukaryotic gene promoters. Here, for the first time, we characterized the function ofthe Arabidopsis NFYA1factor.(1) NFYA1is specifically locate in the nucleus of Arabidopsis root cells, it is a typicalnuclear transcription factor. Expression patterns analysis of NFYA1are multiple, and NFYA1could respond to many environmental stimuli, suggest that NFYA1might be involved indifferent signaling pathways at different developmental stages.(2)35S::NFYA1overexpression lines are hypersensitive to salt and ABA during the seedgermination and early-postgermination growth. And NFYA1is involved in mediatingpostgermination growth under salt stress during a limited developmental window before the seedlings turn green. NFYA1-RNAi line is insensitive to salt stress during seed germinationand postgermination growth. These also suggest that the tolerance to salt stress is consistentwith the NFYA1expression level. Further experiments revealed that the ABA synthesisinhibitor, sodium tungstate could restore the salt sensitivity phenotype of35S:: NFYA1lines.These findings reasonably demonstrate that the endogenous ABA is overproduced in theNFYA1transgenic lines under salt stress and lead to the growth arrest of the germinatedseeds.(3) It is assessed by qRT-PCR that the mRNA levels of ABI3, ABI5as well as thedownstream genes EM1and EM6are significantly upregulated in the developing embryos ofthe35S::NFYA1transgenic lines compared with WT under salt stress. However, compared tonormal condition, higher expression level of ABI3and ABI5was observed in35S::NFYA1transgenic lines under NaCl and ABA treatment, implying that NFYA1might not be the onlyregulator in this pathway. Additionally, it is observed that the RNAi-NFYA1lines showeddecreased level of ABI3, ABI5, EM1and EM6genes indicated that NFYA1may act upstreamof ABI3and ABI5. Furthermore, NFYA1induction is not affected in abi3and abi5mutants.Theses findings demonstrate that ABA induced expression of NFYA1is not dependent onABI3and ABI5, which reinforced our conclusion that NFYA1acts upstream of ABI3andABI5.(4) We provide a reliable model: NFYA1acts upstream of the ABI3-regulated cascadesand negatively controls the postgermination growth during a confined time window, and somecofactors that can bind with NFYA1might also be involved.