Characterization of VvSPL18 and Its Expression in Response to Exogenous Hormones during Grape Berry Development and Ripening.

The sequence and structure of grape SBP-box-like18 (VvSPL18) were identified and characterized to explore its regulatory roles during grape berry development and ripening. Homologous conservation across diverse plant species was observed, and its potential function and modulated roles in grapes were investigated. The results showed that VvSPL18 has an ORF sequence of 1,137 bp, encodes 378 amino acids, and is located on chromosome 14 of grapevine. VvSPL18 has the closest relationship with its homolog in soybeans. The promoter of VvSPL18 contains cis-elements responsive to gibberellins (GA) and salicylic acid (SA), indicating that this gene might respond to these hormones involved in the modulation of grape berry. VvSPL18 is mainly distributed in the nucleus. Expression profiles showed that VvSPL18 is highly expressed only at the veraison stage of the grape berry and is slightly expressed in other phases. RNA-seq data also revealed that VvSPL18 might participate in the modulation of grape berry development and ripening. Treatment with diverse hormones demonstrated that abscisic acid (ABA) had almost no effect on its expression, whereas naphthalene acetic acid (NAA) significantly upregulated its expression at the veraison stage. We also found that VvSPL18 has a GA-responsive cis-element but no NAA-responsive cis-element. GA could promote the expression of VvSPL18 with a peak at an earlier stage than NAA, suggesting that VvSPL18 responds faster to GA than to NAA. This result indicates that VvSPL18 might modulate berry development at this phase through an ABA-independent pathway, and it might directly respond to GA, but indirectly to NAA. Our findings provide insights into the functions of VvSPL18 in mediating grape berry development and ripening.