SSU72 Is Involved In ABA-dependent Dehydration Stress Pathway

Natural plants suffer from a variety of abotic stresses.Drought stress is one of universal abotic stresses,which can cause irreversible damage to plant growth and development as well as severe crop yield reduction.The Abscisic acid(ABA)signaling pathway plays an important role in the drought stress.The drought-stressed plants synthesize a large amount of ABA.After ABA binds to the receptor,SnRK family proteins were released,which,in turn activates downstream transcription factors,like ABF(ABRE binding protein,ABF/AREB).These transcription factors promote the response of downstream genes to drought stress.The SSU72 gene was frist chercterizated in our laboratory.SSU72 encodes a phosphoatase and inhibits the binding of FCA to lcnRNA COOLAIR.SSU72 reduces the accumulation of PRC2 and deposition of H3K27me3 at the FLC,resulting in delaying flowering time.Our studies showed that loss of SSU72 function leads to promoting water loss using detached leaves,suggesting mutation in SSU72 is sensitive to dehydration.These tesults were confirmed with soil drought and mannitol treatment.The stoma size of ssu72 mutant is lager than that of wide type,and the stoma closure was not sensitive to exogenous ABA in ssu72.These observations indicating that SSU72 is involved in the ABA pathway.14-3-3 proteins are conserved in eukaryotes,from yeast to mammalian cell,and plant.14-3-3 proteins are involved in multiple abiotic stresses.Biochemical studies showed that SSU72 interacts with 14-3-3? and 14-3-3?,and 14-3-3? and 14-3-3? interact with transcription factors ABF1,ABF25 ABF3,and ABF4,respectively.The water loss of 14-3-3A?? double mutant is faster than that of wide type and the stoma closure of 14-3-3?? double mutant is not sensitive to ABA treatment.The leaf water loss rate of ssu72 14-3-3?? triple mutant was similar to that of ssu72,indicating that SSU72 and 14-3-3?? are involved in the same pathway.Subcellular localization results showed that SSU72 and ABFs were localized in the nucleus,while 14-3-3? was localized in the cytoplasm and nucleus.We proposed that 14-3-3? is likely to enter the nucleus under drought stress.The transgenic plants containing 14-3-3? fused with GFP were treated with 10 ?M and 15 ?M ABA,and GFP singals were observed in nucleus while these singals were observed in nucleus and cytoplasm without treatment.Pevious study suggested that CRPK1 phosphorylates 14-3-3? under cold stress,and phosphorylated 14-3-3? moved into the nucleus from cytoplasm.14-3-3?-GFP in the crpk1 was also treated with 10 ?M and 15 ?M ABA,GFP signals were observed in nucleus and cytoplasm,suggesting that CRPK1 is critical for 14-3-3? movement from cytoplasm to nucleus.Further studies showed that water loss of the crpk1 is faster than that of Col-0,indicating that CRPK1 is also involved in the drought stress pathway.