Transcription factor VviWOX13C regulates fruit set by directly activating VviEXPA37/38/39 in grape (Vitis vinifera L).

VviWOX13C plays a key regulatory role in the expansin during fruit set. Expansins as a type of non-enzymatic cell wall proteins, are responsible for the loosening and extension in cell walls leading to the enlargement of the plant cells. However, the current studies are still lacking in expansin genes associated with promoting fruit set. Here, 29 members of the expansin gene family were identified in the whole genome of grapes (Vitis vinifera L.), and the functional prediction of expansins was based on the gene annotated information. Results showed that the 29 members of grape expansin gene family could be mainly divided into four subfamilies (EXPA, EXPB, LIKE A, and LIKE B), distributed on 16 chromosomes. Replication analysis showed that there were four segmental duplications and two tandem duplications. Each expansins sequence contained two conserved domain features of grape EXPs (DPBB_1 and Expansin_C) through protein sequence analysis. The transcriptome sequencing results revealed that VviEXPA37, VviEXPA38, and VviEXPA39 were induced and upregulated by CPPU. Furthermore, transcriptional regulatory prediction network indicated that VviWOX13C targeted regulates VviEXPA37, VviEXPA38, and VviEXPA39 simultaneously. EMSA and dual luciferase assays demonstrated that VviWOX13C directly activated the expression of VviEXPA37, VviEXPA38, and VviEXPA39 by directly binding to its promoter. These results provide a basis for further studies on the function and regulatory mechanisms of expansin genes in fruit set.