College of Horticulture, South China Agricultural University, Guangzhou, P. R. China.
Plant J. 2024 Aug;119(3):1353-1368. doi: 10.1111/tpj.16855. Epub 2024 Jun 3.
Cucumber plants are highly susceptible to the hemibiotroph oomycete Phytophthora melonis. However, the mechanism of resistance to cucumber blight remains poorly understood. Here, we demonstrated that cucumber plants with impairment in the biosynthesis of brassinosteroids (BRs) or gibberellins (GAs) were more susceptible to P. melonis. By contrast, increasing levels of endogenous BRs or exogenously application of 24-epibrassinolide enhanced the resistance of cucumber plants against P. melonis. Furthermore, we found that both knockout and overexpression of the BR biosynthesis gene CYP85A1 reduced the endogenous GA content compared with that of wild-type plants under the condition of inoculation with P. melonis, and the enhancement of disease resistance conferred by BR was inhibited in plants with silencing of the GA biosynthetic gene GA20ox1 or KAO. Together, these findings suggest that GA homeostasis is an essential factor mediating BRs-induced disease resistance. Moreover, BZR6, a key regulator of BR signaling, was found to physically interact with GA20ox1, thereby suppressing its transcription. Silencing of BZR6 promoted endogenous GA biosynthesis and compromised GA-mediated resistance. These findings reveal multifaceted crosstalk between BR and GA in response to pathogen infection, which can provide a new approach for genetically controlling P. melonis damage in cucumber production.
黄瓜植株极易感染半活体卵菌病原菌——甜瓜疫霉。然而，黄瓜对疫病的抗性机制仍不清楚。本研究表明，在生物合成过程中受到 BR（油菜素内酯）或 GA（赤霉素）抑制的黄瓜植株更容易感染甜瓜疫霉。相反，内源 BR 水平的提高或外源施用 24-表油菜素内酯均可增强黄瓜植株对甜瓜疫霉的抗性。此外，我们发现，与野生型植株相比，CYP85A1（BR 生物合成基因）的敲除和过表达均降低了接种甜瓜疫霉时的内源 GA 含量，而 BR 增强的抗病性在沉默 GA 生物合成基因 GA20ox1 或 KAO 的植株中受到抑制。综上所述，这些结果表明 GA 动态平衡是 BR 诱导的抗病性的一个重要因素。此外，BR 信号转导的关键调控因子 BZR6 被发现与 GA20ox1 发生物理相互作用，从而抑制其转录。BZR6 的沉默促进了内源 GA 的生物合成，并损害了 GA 介导的抗性。这些发现揭示了 BR 和 GA 之间在应对病原菌感染时的复杂相互作用，为在黄瓜生产中通过遗传手段控制甜瓜疫霉的破坏提供了一种新的方法。
