The intrinsic developmental age signal defines an age-dependent climbing behavior in cucumber

Abstract

The tendril is a climbing organ in cucurbits and functions in physical support and to avoid shading by neighboring vegetation. However, how cucurbits produce tendrils to obtain climbing ability is largely unknown. In this study, tendril phenotypes were investigated during different developmental stages. Our results revealed that tendril growth exhibited an age-dependent pattern in cucurbits. Tendril growth was inhibited, and the tendril was formed as a short tendril [nonfunctional tendril (nonF-tendril), approximately 0.1 cm] during the seedling stage. In contrast, enhanced cell proliferation and cell expansion led to rapid elongation of the tendril during the climbing stage, and the tendril formed as a functional tendril (F-tendril, approximately 30 cm) to obtain climbing ability. RT-qPCR detection showed that age-dependent tendril growth correlated negatively with the abundance of the conserved age regulator CsmiR156. Defoliation induced CsmiR156 to inhibit CsSPLs, and F-tendril formation and climbing ability were delayed in defoliated cucumbers, which confirmed the role of CsmiR156 in regulating tendril growth in vivo. Additionally, exogenous gibberellin (GA) treatment showed that GA positively regulated tendril growth, and RT-qPCR detection showed that the GA bio-synthetic genes and metabolic genes were affected by age pathway, suggesting that the age pathway depended on GA bio-synthetic and metabolic pathway to regulate cell expansion to determine tendril growth. In summary, our work reveals that change in tendril type is an important marker of phase transition in cucumber, and tendril growth is regulated by an intrinsic developmental age signal, ensuring that the cucumber obtains climbing ability at a suitable age.