Touch‐Responsive <i>CsaGASAs</i> Regulate Tendril Length During the Climbing Stage in Cucumber

Touch stimuli are a form of environmental stress or signaling that can modify plant growth. As touch-sensitive organs, tendrils can sense touch stimuli and change their growth. Here, three Gibberellic Acid-Stimulated Arabidopsis family members (CsaGASAs) were identified as touch-responsive genes in tendrils, with their expression regulated by touch stimuli via GA signaling. CsaGASA3 and CsaGASA9 (belonging to the A1 clade) were up-regulated by touch stimuli, whereas CsaGASA5 (belonging to the C1 clade) was highly expressed in untouched tendrils and down-regulated by touch stimuli. CsaGASA3 was localized to the cell periphery and nucleus, and it acted as a repressor of tendril elongation. In contrast, CsaGASA5 was localized to the cell periphery and nuclear periphery, and it acted as an activator of tendril elongation. Yeast two-hybrid, luciferase complementation, and Co-IP assays showed that CsaGASA3 interacts with two xyloglucan endotransglucosylase/hydrolases (CsaXTH2 and CsaXTH29). CsaXTH2 and CsaXTH29 were localized to the cell periphery and positively regulated tendril elongation. In summary, our work suggests that touch stimuli depend on GA deactivation to induce the repressor (CsaGASA3) and to inhibit the activator (CsaGASA5) of tendril elongation. Thereafter, these antagonistically acting GASA peptides finely regulate tendril elongation to obtain a suitable tendril length in cucumber.