Brassinosteroids Regulate the Water Deficit and Latex Yield of Rubber Trees

Brassinolide (BR) is an important plant hormone that regulates the growth and development of plants and the formation of yield. The yield and quality of latex from Hevea brasiliensis are regulated by phytohormones. The understanding of gene network regulation mechanism of latex formation in rubber trees is still very limited. In this research, the rubber tree variety CATAS73397 was selected to analyze the relationship between BR, water deficit resistance, and latex yield. The results showed that BR improves the vitality of rubber trees under water deficit by increasing the rate of photosynthesis, reducing the seepage of osmotic regulatory substances, increasing the synthesis of energy substances, and improving the antioxidant system. Furthermore, BR increased the yield and quality of latex by reducing the plugging index and elevating the lutoid bursting index without decreasing mercaptan, sucrose, and inorganic phosphorus. This was confirmed by an increased expression of genes related to latex flow. RNA-seq analysis further indicated that DEG encoded proteins were enriched in the MAPK signaling pathway, plant hormone signal transduction and sucrose metabolism. Phytohormone content displayed significant differences, in that trans-Zeatin, ethylene, salicylic acid, kinetin, and cytokinin were induced by BR, whereas auxin, abscisic acid, and gibberellin were not. In summary, the current research lays a foundation for comprehending the molecular mechanism of latex formation in rubber trees and explores the potential candidate genes involved in natural rubber biosynthesis to provide useful information for further research in relevant areas.