Role of phytosterols in olive flower opening and early fruit development

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). In this report, the profiling of phytosterol measurement revealed that β‐sitosterol is the most abundant in olive reproductive organs.
Our data demonstrated that both OeCYP51 and OeSMT2 genes were upregulated during floral anthesis, which is in 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 showed 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 indicated an upregulation of β‐sitosterol biosynthesis by BR at the transcriptional level during early olive fruit growth, hence providing a valuable tool to unravel the physiological function of SMT2 in future studies.

XXXI International Horticultural Congress (IHC2022): International Symposium on Breeding and Effective Use of Biotechnology and Molecular Tools in Horticultural Crops

J. Corbacho, C. Inês, J. Labrador, A. Cordeiro, M.C. Gomez-Jimenez

brassinosteroid, campesterol, early fruit growth, gene expression, sterol 14 alpha-demethylases, sterol 24-C-methyltransferase, sitosterol

https://doi.org/10.17660/ActaHortic.2023.1362.46