Differential expression of genes in olive leaves and buds of ON- versus OFF-crop trees

Abstract

Alternate bearing (AB) refers to the tendency of trees to have an irregular crop load from 1 year (ON) to the next year (OFF). Despite its economic importance, it is not fully understood how gene networks and their related metabolic pathways may influence the irregular bearing in olive trees. To unravel molecular mechanisms of this phenomenon in olive (cv. Conservalia), the whole transcriptome of leaves and buds from ON and OFF-trees was sequenced using Illumina next generation sequencing approach. The results indicated that expressed transcripts were involved in metabolism of carbohydrates, polyamins, phytohormones and polyphenol oxidase (POD) related to antioxidant system. Expression of POD was increased in leaf samples of ON- versus OFF-trees. The expression pattern of the greater number of genes was changed more in buds than in leaves. Up-regulation of gene homologues to the majority of enzymes that were involved in photorespiration metabolism pathway in buds of ON-trees was remarkable that may support the hypotheses of an increase in photorespiratory metabolism in these samples. The results indicated changes in expression pattern of homologous to those taking part of abscisic acid and cytokinin synthesis which are connected to photorespiration. Our data did not confirm expression of homologue (s) to those of chlorogenic acid metabolism, which has been addressed earlier that have a probable role in biennial bearing in olive. Current findings provide new candidate genes for further functional analysis, gene cloning and exploring of molecular basses of AB in olive.

A Complex Gene Network Mediated by Ethylene Signal Transduction TFs Defines the Flower Induction and Differentiation in Olea europaea L.

“…However, our strategy aims to better promote the focus on differential expressed genes that could link flower induction and differentiation. In our opinion, this approach might justify the lower number of DEG between ‘ON’ and ‘OFF’ compared to those observed by Dastkar and colleagues [ 28 ].…”

“…Our analyses also highlighted a significant up-regulation of carbohydrate metabolic/transport function in July and March ‘OFF’ samples (‘ON’-buds for return bloom) ( Table 2 ). A relationship between carbohydrates metabolism and the biennial bearing in olive tree has already been reported [ 28 , 65 , 66 ]. Indeed, carbohydrate availability fluctuation was suggested as a key factor triggering alternate bearing by the inhibition of flower buds that occur when carbohydrate storage is reduced, which is usually recorded after a high crop production [ 7 , 67 ].…”

“…Recently, a whole transcriptome sequencing in the olive cv. Conservalia highlighted the molecular mechanisms behind this phenomenon at flower induction [ 28 ]. Here, we analyzed the different transcriptomic profiles of lateral buds from both loaded (‘ON’) and unloaded (‘OFF’) branches in the same olive tree in July (flower induction) and the following March (flower differentiation); it is useful to highlight a relationship between flower induction and differentiation in terms of DEGs.…”

“…The phenylpropanoids over-produced in stressful conditions are reported to be synthesized in response to photo-assimilated excess, which could occur under Long Day (LD) condition [ 70 ]. An increased expression level of the transcripts related to flavonoid biosynthesis in the ‘OFF’ compared to ‘ON’ year leaves was reported in the olive tree [ 28 , 66 , 71 ].…”

“…Further, the sequencing, assembly, and annotation of olive genome should provide a valuable resource for new insight into the genetic control of physiological and developmental processes and pivotal phenotypic complex traits of olive tree [ 25 , 26 , 27 ]. Very recently, a differential transcriptomic analysis between ‘ON’ and ‘OFF’ buds and leaves revealed the involvement of the metabolism of carbohydrates, polyamines, phytohormones, and polyphenol oxidase correlated to antioxidant system in the alternate bearing in olive tree [ 28 ]. Here, we lead to identify differential expressed genes during the switch from the vegetative to the reproductive phase of the lateral buds in the olive cv.…”