Membrane Steroid Binding Protein 1 （MSBP1）Stimulates Tropism by Trafficking and Auxin Regulating Vesicle Redistribution  

作　　者：Xi Yang Li Song Hong-Wei Xue 

机构地区：[1]National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy ofSciences, 300 Fenglin Road, 200032 Shanghai, China

出　　处：《Molecular Plant》2008年第6期1077-1087,共11页分子植物（英文版）

基　　金：This work was supported by the National Natural Science Foundation of China （No. 90717001, 30721061, 30425029） and Science and Technology Commission of Shanghai Municipality （08XD14049）.We thank Jian Xu （Utrecht University, Netherlands） for providing Arabidopsis seeds containing DR5-GUS and PIN2-EGFP expression cassettes. No conflict of interest declared,

摘　　要：Overexpression of membrane steroid binding protein 1 （MSBP1） stimulates the root gravitropism and antigravitropism of hypocotyl, which is mainly due to the enhanced auxin redistribution in the bending regions of hypocotyls and root tips. The inhibitory effects by 1-N-naphthylphthalamic acid （NPA）, an inhibitor of polar auxin transport, are suppressed under the MSBP1 overexpression, suggesting the positive effects of MSBP1 on polar auxin transport. Interestingly, sub-cellular localization studies showed that MSBP1 is also localized in endosomes and observations of the membraneselective dye FM4-64 revealed the enhanced vesicle trafficking under MSBP1 overexpression. MSBPl-overexpressing seedlings are less sensitive to brefeldin A （BFA） treatment, whereas the vesicle trafficking was evidently reduced by suppressed MSBP1 expression. Enhanced MSBP1 does not affect the polar localization of PIN2, but stimulates the PIN2 cycling and enhances the asymmetric PIN2 redistribution under gravi-stimulation. These results suggest that MSBP1 could enhance the cycling of PIN2-containing vesicles to stimulate the auxin redistribution under gravi-stimulation, providing informative hints on interactions between auxin and steroid binding protein.Overexpression of membrane steroid binding protein 1 （MSBP1） stimulates the root gravitropism and antigravitropism of hypocotyl, which is mainly due to the enhanced auxin redistribution in the bending regions of hypocotyls and root tips. The inhibitory effects by 1-N-naphthylphthalamic acid （NPA）, an inhibitor of polar auxin transport, are suppressed under the MSBP1 overexpression, suggesting the positive effects of MSBP1 on polar auxin transport. Interestingly, sub-cellular localization studies showed that MSBP1 is also localized in endosomes and observations of the membraneselective dye FM4-64 revealed the enhanced vesicle trafficking under MSBP1 overexpression. MSBPl-overexpressing seedlings are less sensitive to brefeldin A （BFA） treatment, whereas the vesicle trafficking was evidently reduced by suppressed MSBP1 expression. Enhanced MSBP1 does not affect the polar localization of PIN2, but stimulates the PIN2 cycling and enhances the asymmetric PIN2 redistribution under gravi-stimulation. These results suggest that MSBP1 could enhance the cycling of PIN2-containing vesicles to stimulate the auxin redistribution under gravi-stimulation, providing informative hints on interactions between auxin and steroid binding protein.

关 键 词：MSBP1 polar auxin transport auxin response GRAVITROPISM vesicle trafficking. 

分 类 号：Q946.885.1[生物学—植物学] O647.2[理学—物理化学]