Regulation of sterol content and biosynthetic gene expression during flower opening and early fruit development in olive

Abstract

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 analyzed 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 -sitosterol is the most abundant in olive reproductive organs. Our data demonstrate that both OeCYP51 and OeSMT2 genes are upregulated during floral anthesis in good agreement with the rise in cholesterol and -sitosterol contents in olive flower. 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 -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 up-regulation of -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.

Associations between Oil Yield and Profile of Fatty Acids, Sterols, Squalene, Carotenoids, and Tocopherols in Seed Oil of Selected Japanese Quince Genotypes during Fruit Development

“…The lack of squalene presence was also reported in the olive flowers, where substantial content of sterols was found, while olive oil ( Olea europaea L.) is one of the richest sources of sterols and squalene. [ 17 ] In the last three measurement points, the concentration of squalene did not differ statistically significant within each genotype (86th, 100th, and 114th DAFB). A similar as for sterols, the recorded concentration of squalene in seed oil from mature seeds (114th DAFB) was twofold higher (nearly) than in previous reports.…”

Authenticity in Olive Oils from an Empeltre Clonal Selection in Aragon (Spain): How Environmental, Agronomic, and Genetic Factors Affect Sterol Composition

“…The evolution of sterols directly in the olive pulp [ 50 ] has been less studied, but increases in sterol concentration have indeed been observed in the pulp as ripening progresses. Inês et al [ 51 ] suggested that the increase they observed in sterol biosynthesis in early fruits was because the rates of mitosis and membrane formation were at maximum levels. The complexity of the enzymatic pathways involved in sterol biosynthesis [ 52 , 53 ] and the participation of sterols in the biosynthesis of other compounds [ 37 , 54 ], as well as abiotic stress effects on olives (a less studied factor) [ 53 , 55 ], generate a wide range of variability in sterol concentration throughout ripening.…”

Characterization of Transcriptome Dynamics during Early Fruit Development in Olive (Olea europaea L.)

“…Olive trees ( Olea europaea L.) of the ‘Picual’ cultivar 20 years old in an orchard under drip irrigation (fertigation with suitable liquid fertilizers) near Badajoz (Spain) were studied. From these trees, flowers were collected at the anthesis stage (0 days post-anthesis, DPA) and fruits were sampled at 7, 14, 21, 28, 35, and 42 DPA, spanning a time from the fruit set to the time of endocarp lignification, and 500 flowers or fruits for each developmental stage during the 2018–2019 growing seasons [ 27 , 62 , 63 ]. Harvested flowers and whole fruits of ‘Picual’ olive were weighed, and the longitudinal and transverse diameters were measured at different developmental stages ( Figure 1 ).…”

“…Moreover, the application of exogenous brassinosteroid (BR) promoted early fruit growth in olive, whereas blocking BR synthesis with brassinazole (Brz) slowed down the fruit growth rate [ 62 ]. Likewise, the data have provided new findings on the role of BRs in modulating the composition and gene expression of sterols and sphingolipids, these being lipophilic membrane components essential for cellular functions during early olive fruit growth [ 62 , 63 ]. This latter study also revealed the upregulation of β -sitosterol biosynthesis by BR at the transcriptional level during early olive fruit growth.…”