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 the BIGs expression patterns showed that BIG3 and BIG5 have similar expression patterns. big5-1 displayed a dwarf growth and big3-1 big5-1 double mutant showed more severe defects, indicating functional redundancy between BIG3 and BIG5. Moreover, both big5-1 and big3-1 big5-1 exhibited a reduced sensitivity to Brassinosteroid (BR) treatment. Brefeldin A (BFA)-induced BR receptor Brassinosteroid insensitive 1 (BRI1) aggregation was reduced in big5-1 mutant, indicating that the action of BIG5 is required for BRI1 recycling. Furthermore, BR-induced dephosphorylation of transcription factor BZR1 was decreased in big3-1 big5-1 double mutants. The introduction of the gain-of-function of BZR1 mutant BZR1-1D in big3-1 big5-1 mutants can partially rescue the big3-1 big5-1 growth defects. Our findings revealed that BIG5 functions redundantly with BIG3 in plant growth and gravitropism, and BIG5 participates in BR signal transduction pathway through regulating BRI1 trafficking.
Highlights
ADP-ribosylation factors (ARFs), are small G proteins that function in endomembrane trafficking
The dephosphorylation level of BZR1 was decreased in BR-treated big5-1 compared to wild-type plants. These results showed that BIG5 functions in regulating plant growth and gravitropism partially through mediating Brassinosteroid insensitive 1 (BRI1) recycling and subsequent BR signaling transduction pathway
The big1-1, big2-1, big3-1, and big4-1 mutants showed similar overall seedling size compared to wild-type plants (Figure 1), whereas, the big5-1 mutant had smaller overall growth size compared to wild-type plants, displaying reduced rosette leaf size and inflorescence height (Figure 1 and Figure S2A–K)
Summary
ADP-ribosylation factors (ARFs), are small G proteins that function in endomembrane trafficking. ARF-GEFs can be classified into GBF1 and BIG subfamilies [1,2]. In Arabidopsis, reports have shown that GNOM and GNOM-LIKE1, members of GBF1-subfamily, are involved in internal trafficking of auxin transporter PIN-FORMED (PIN) proteins [3,4,5,6,7,8,9] and brassinosteroid (BR) receptor BRI1 [10,11]. The functions of BIG-subfamily ARF-GEFs (BIG1–BIG5) in plant growth and development have not been fully investigated. The ben mutants had short roots and displayed defective polar distribution of PIN1 and PIN2, affecting PIN-mediated auxin transport for organ development and gravitropism [4,15]. Whether and how BIG5 and other members of BIG subfamily take part in plant growth and gravitropic response remain unknown
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