Cucumber JASMONATE ZIM-DOMAIN 6 interaction with transcription factor MYB6 impairs waterlogging-triggered adventitious rooting.

Waterlogging is a serious abiotic stress that drastically decreases crop productivity by damaging the root system. Jasmonic acid (JA) inhibits waterlogging-induced adventitious root (AR) formation in cucumber (Cucumis sativus L.). However, we still lack a profound mechanistic understanding of how JA governs AR formation under waterlogging stress. JAZ (JASMONATE ZIM-DOMAIN) proteins are responsible for repressing JA signaling in a transcriptional manner. In this study, we showed that overexpressing CsJAZ8 inhibited the formation of ARs triggered by waterlogging. Molecular analyses revealed that CsJAZ8 inhibited the activation of the R2R3-MYB transcription factor CsMYB6 via direct interaction. Additionally, silencing of CsMYB6 negatively impacted AR formation under waterlogging stress, as CsMYB6 could directly bind to the promoters of 1-aminocyclopropane-1-carboxylate oxidase2 gene CsACO2 and gibberellin 20-oxidases gene CsGA20ox2, facilitating the transcription of these genes. The overexpression of CsACO2 and CsGA20ox2 led to increased levels of ethylene and gibberellin, which facilitated AR formation under waterlogging conditions. On the contrary, silencing these genes resulted in contrasting phenotypes of AR formation. These results highlight that the transcriptional cascade of CsJAZ8 and CsMYB6 plays a critical role in regulating hormonal-mediated cucumber waterlogging-triggered AR formation by inhibiting ethylene and gibberellin accumulation. We anticipate that our findings will provide insights into the molecular mechanisms that drive the emergence of AR in cucumber plants under waterlogging stress.

Cucumber CsTRY Negatively Regulates Anthocyanin Biosynthesis and Trichome Formation When Expressed in Tobacco.

The development of trichomes (spines) on cucumber fruits is an important agronomic trait. It has been reported that two MYB family members, CsMYB6 (Csa3G824850) and CsTRY (Csa5G139610) act as negative regulators of trichome or fruit spine initiation. To further study the functions of these two genes, we overexpressed them in tobacco, and found that the flowers and seed coats of transformants overexpressing CsTRY displayed an unexpected defect in pigmentation that was not observed in plants overexpressing CsMYB6. Moreover, the expression of key genes in the flavonoid synthesis pathway was repressed in CsTRY overexpressing plants, which resulted in the decrease of several important flavonoid secondary metabolites. In addition, CsTRY could interact with the AN1 homologous gene CsAN1 (Csa7G044190) in cucumber, which further confirmed that CsTRY not only regulates the development of fruit spines, but also functions in the synthesis of flavonoids, acting as the repressor of anthocyanin synthesis.