The Preliminary Study Of Function Of Arabidopsis Gene SAV9

In addition to providing energy for plant photosynthesis,light is an important environmental signal that regulates plant growth and development.When plants are in high density,they will sense the change of light quality and produce a series of plastic changes in order to compete for limited light resources.These changes,which are collectively called Shade Avoidance Syndrome(SAS),include elongation of stem/hypocotyl and petiole,elevated hyponasty of leaves,early flowering and reduced chlorophyll content,etc.In this study,the role of SAV9 in shade avoidance responses was investigated using a T-DNA insertion mutant sav9 and simulated shade condition with R:FR(red:far-red light)ratio around 0.6.Through a series of phenotypic study,we found that sav9 mutant plants had defects in hypocotyl elongation after shade treatment,but not in shade-induced reduction in chlorophyll content,suggesting that SAV9 may regulate a subset of shade avoidance responses.In addition,adult sav9 mutant showed early flowering phenotype,suggesting that SAV9 may also be involved in the regulation of flowering time.Shade treatment induces the expression of SAV9 mRNA,which is COP 1-dependent.In addition,we found that the expression of SAV9 was negatively regulated by the brassinosteroid(BR)pathway.We examined the expression of PAR1 and HFR1,genes that negatively regulate the shade avoidance responses,in sav9 mutants,and found that SAV9 negatively regulates the expression of HFR1 after short-term shade treatment.It suggests that SAV9 may be involved in the light signaling pathway.To explore the relationship between the shade phenotype of sav9 and growth-promoting hormones,we examined the responses of sav9 to epi-brassinolide(eBL),Picloram(an auxin analogue)and GA3.We found that under shade condition,none of the three hormones could restore the short hypocotyl phenotype of sav9 mutant,indicating that the hypocotyl elongation defect of sav9 was not caused by insufficient hormone content.Under normal white light condition,the sensitivity of sav9 mutant to all three hormones was lower than that of the wild type,indicating that SAV9 may act downstream of these hormones,and are required for hypocotyl elongation.In consistent with this hypothesis,we also found that hypocotyl length of sav9 mutant seedlings grown in dark was also slightly shorter than that of the wild type.In addition,mutation in SAV9 does not affect shade-regulated expression of downstream reporter genes of these hormones,or genes involved in the biosynthesis or signal transduction of these hormones.Plant cells have cell walls,and cell elongation requires cell wall relaxation.Shading induces the expression of a range of genes involved in cell wall modifications.So far,we have examined the expression of XTR7 and XTH17 in sav9 upon shade treatment.We found that SAV9 did not affect the early induction of XTR7 and XTH17 by shading,which needs further experimental verification.