Integrated transcriptome-metabolome analysis reveals oleanolic acid as a central regulator of heat stress adaptation...

Alpine rhododendron has high ornamental value because of its vibrant color. However, growing them in urban landscapes is challenging, as high temperatures can slow the growth of Rhododendron roots and cause leaf burning. At present, the metabolic pathways involved in the response of Rhododendron to heat stress are still poorly understood. Rhododendron moulmainense has all the characteristics of alpine Rhododendron; however, its heat tolerance is relatively strong.

Here, we report the systematic response of R. moulmainense to high-temperature stress. Combined analysis of the transcriptome and metabolome revealed that under high-temperature stress, the tryptophan and terpenoid metabolic pathways were significantly activated in the leaves and roots of R. moulmainense. Additionally, the levels of the triterpenoid compound oleanolic acid and its isomer ursolic acid, which have antioxidant effects, were significantly increased under high-temperature stress conditions. Moreover, the levels of these compounds were significantly increased in the roots of R. moulmainense with good growth. Furthermore, exogenous oleanolic acid application experiments verified that oleanolic acid can significantly increase the heat tolerance of R. moulmainense. In addition, a combination of trend analysis and cis-acting element analysis revealed that MYB transcription factors may be key regulatory factors involved in regulating the synthesis of oleanolic acid and the response to high-temperature stress.

Integrated transcriptomic and metabolomic analyses revealed that high-temperature stress activates tryptophan and terpenoid metabolism in R. moulmainense. Notably, oleanolic acid plays an important role in regulating environmental adaptability, and MYB might a key regulator of oleanolic acid biosynthesis under heat stress. These findings provide valuable insights into the molecular basis of thermotolerance in alpine rhododendrons and offer potential targets for domestication and breeding of heat-resilient cultivars.