Abstract

ADP-ribosylation factor-guanine nucleotide exchange factors (ARF-GEFs) act as key regulators of vesicle trafficking in all eukaryotes. In Arabidopsis, there are eight ARF-GEFs, including three members of the GBF1 subfamily and five members of the BIG subfamily. These ARF-GEFs have different subcellular localizations and regulate different trafficking pathways. Until now, the roles of these BIG-subfamily ARF-GEFs have not been fully revealed. Here, analysis of theBIGsexpression patterns showed thatBIG3andBIG5have similar expression patterns.big5-1displayed a dwarf growth andbig3-1 big5-1double mutant showed more severe defects, indicating functional redundancy betweenBIG3andBIG5. Moreover, bothbig5-1andbig3-1 big5-1exhibited a reduced sensitivity to Brassinosteroid (BR) treatment. Brefeldin A (BFA)-induced BR receptor Brassinosteroid insensitive 1 (BRI1) aggregation was reduced inbig5-1mutant, indicating that the action of BIG5 is required for BRI1 recycling. Furthermore, BR-induced dephosphorylation of transcription factor BZR1 was decreased inbig3-1 big5-1double mutants. The introduction of the gain-of-function ofBZR1mutantBZR1-1Dinbig3-1 big5-1mutants can partially rescue thebig3-1 big5-1growth defects. Our findings revealed that BIG5 functions redundantly with BIG3 in plant growth and gravitropism, andBIG5participates in BR signal transduction pathway through regulating BRI1 trafficking.Keywords:ARF protein;BIG family ARF-GEF;auxin;brassinosteroids;gravity response