title: Membrane steroid binding protein 1 (MSBP1) stimulates tropism by regulating vesicle trafficking and auxin redistribution.
abstract: Overexpression of membrane steroid binding protein 1 (MSBP1) stimulates the root gravitropism and anti-gravitropism 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 membrane-selective dye FM4-64 revealed the enhanced vesicle trafficking under MSBP1 overexpression. MSBP1-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.
authors.affiliation: Chinese Academy of Sciences, 200032 Shanghai, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Yang
authors.forename: Li
authors.initials: L
authors.lastname: Song
authors.forename: Hong-Wei
authors.initials: HW
authors.lastname: Xue
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D020126:Brefeldin A / Q000494:pharmacology; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D022162:Cytoplasmic Vesicles / Q000187:drug effects / Q000378:metabolism*; D004705:Endocytosis / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018522:Gravitropism / Q000187:drug effects / Q000502:physiology*; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D020126:Brefeldin A; D002352:Carrier Proteins; D007210:Indoleacetic Acids; C504785:MSBP1 protein, Arabidopsis; C117013:AT5G57090 protein, Arabidopsis; C030737:indoleacetic acid