S01 - Session P6 - Role of phytosterol in olive flower opening and early fruit development

Authors: Carla Inês, Jorge Corbacho, Beatriz Briegras, Maria-Carmen Camarero, Juana Labrador, Antonio Cordeiro, María Carmen Gomez-Jimenez *

Phytosterols are lipophilic membrane components essential not only for diverse cellular functions but also are biosynthetic precursors of the plant hormone brassinosteroid (BR). However, the interaction between phytosterol and BR during early fleshy fruit growth remains largely uncharacterized. In olive, phytosterols are important lipids because they affect oil quality, but phytosterol composition during flowering and early fruit development has not been explored. Here, we first investigated the temporal changes in phytosterol composition and biosynthetic gene expression that occurred during olive flower opening and early fruit growth. Next, we analysed the interrelationship between phytosterol and BR, whose levels we manipulated through the application of exogenous BRs (24‐epibrassinolide, EBR) or a BR biosynthesis inhibitor (brassinazole, Brz). The profiling of the phytosterol measurements revealed that β‐sitosterol is the most abundant in olive reproductive organs. Our data demonstrate that both the OeCYP51 and OeSMT2 genes are upregulated during floral anthesis in good agreement with the rise in cholesterol and β‐sitosterol contents in olive flowers. By contrast, the OeCYP51 and OeSMT2 genes displayed different expression patterns during early olive fruit development. Furthermore, our data show that exogenous EBR enhanced the early olive fruit growth, as well as the OeSMT2 transcript and β‐sitosterol levels, but decreased the OeCYP51 transcript, squalene, campesterol, and cholesterol levels, whereas the Brz treatment exerted the opposite effect. Overall, our findings indicate an upregulation of β‐sitosterol biosynthesis by BR at the transcriptional level during early olive fruit growth, providing a valuable tool to unravel the physiological function of SMT2 in future studies