The Function Of Shade Avoidance Related Gene SAV4 In Auxin Transport In Arabidopsis Thaliana

Auxin is a very important phytohormone and it is involved in essentially every stages of plant growth and development.The auxin concentration gradient formed and maintained by auxin polarity transport affects the growth and differentiation of plant tissues and organs.The current study shows that shade avoidance and tropic responses in Arabidopsis are related to the transport and distribution of auxin.Our laboratory have identified sav4(shade avoidence 4)as a mutant impaired in shade-induced hypocotyl in simulated shade.Previous work demonstrated that SAV4 was polarly localized in the cell membrane facing the shootward side and nucleus.And SAV4 could influence auxin polar transport.In this study,we study the positioning of SAV4 and its function in auxin transport.First,we found that deletion of the predicted N-terminal and C-terminal nuclear localization signal sequences of SAV4 protein did not alter the nuclear localization of the protein.Interestingly,SAV4 with loss of the C-terminal nuclear localization signal sequence could not rescue sav4 hypocotyl phenotypes in simulated shade and its polar membrane localization have changed.This result indicate that the 598-631 amino acid sequence is very important for the polar cell membrane localization and function of SAV4.In addition,the palmitoylation modification of SAV4 protein was verified by our experiments.And mutations at the N-terminal predicted palmitoylation sites have no significant effect on subcellular localization and function of SAV4.Second,both Pull down and BiFC demonstrated that SAV4 interacted directly with ABCB1c.Mutation of SAV4 did not affect the cell membrane localization of ABCB1.Mutations neither in ABCB1 nor in ABCB19 did not affect the localization of SAV4.Accidentally,SAV4 was able to rescue abcbl9 hypocotyl phenotypes in simulated shade suggesting that SAV4 may be involved in the ABCB 19 signaling pathway that regulates hypocotyl elongation in shade and worked downstream of ABCB 19.Finally,we conducted preliminary studies on the relationship between the strong hypocotyl gravitrpism and auxin levels in sav4 mutants under dark conditions.We have found that the level of auxin in the sav4 hypocotyl under dark conditions did not directly affect its negative gravity response.