Analysis of transcripts differentially expressed between fruited and deflowered ‘Gala’ adult trees: a contribution to biennial bearing understanding in apple

Abstract

BackgroundThe transition from vegetative to floral state in shoot apical meristems (SAM) is a key event in plant development and is of crucial importance for reproductive success. In perennial plants, this event is recurrent during tree life and subject to both within-tree and between-years heterogeneity. In the present study, our goal was to identify candidate processes involved in the repression or induction of flowering in apical buds of adult apple trees.ResultsGenes differentially expressed (GDE) were examined between trees artificially set in either ‘ON’ or ‘OFF’ situation, and in which floral induction (FI) was shown to be inhibited or induced in most buds, respectively, using qRT-PCR and microarray analysis. From the period of FI through to flower differentiation, GDE belonged to four main biological processes (i) response to stimuli, including response to oxidative stress; (ii) cellular processes, (iii) cell wall biogenesis, and (iv) metabolic processes including carbohydrate biosynthesis and lipid metabolic process. Several key regulator genes, especially TEMPRANILLO (TEM), FLORAL TRANSITION AT MERISTEM (FTM1) and SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) were found differentially expressed. Moreover, homologs of SPL and Leucine-Rich Repeat proteins were present under QTL zones previously detected for biennial bearing.ConclusionsThis data set suggests that apical buds of ‘ON’ and ‘OFF’ trees were in different physiological states, resulting from different metabolic, hormonal and redox status which are likely to contribute to FI control in adult apple trees. Investigations on carbohydrate and hormonal fluxes from sources to SAM and on cell detoxification process are expected to further contribute to the identification of the underlying physiological mechanisms of FI in adult apple trees.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0739-y) contains supplementary material, which is available to authorized users.

Impact of within-tree organ distances on floral induction and fruit growth in apple tree: implication of carbon and gibberellin organ contents

“…In addition, in the hydroxylating pathway, GA1 was slightly higher in non-fruiting tree parts and in OFF trees (supplementary material Figure S5) whereas GA8 slightly accumulated in fruit presence. Altogether these results are consistent with the down-regulation of MdGA2ox transcripts in OFF trees (or its up-regulation in ON trees), observed in Guitton et al, (2016). They suggest that the last steps of GA catabolism could be less active in absence of fruit (conversely more active in presence of fruit).…”

“…In the apple tree, GA4 has been assumed to move from fruit to SAM in apple tree (Ramírez et al , 2004). The involvement of GA in FI control was further confirmed by differential expressions of genes involved in the GA biosynthesis pathway (GA20ox and GA2ox) in SAM of apple trees with heavy or low crop loads (Guitton et al , 2016). This study also suggested a context of carbohydrate starvation, in SAM of trees in high cropping conditions.…”

SVP-like MADS Box Genes Control Dormancy and Budbreak in Apple

“…To address their potential roles in early apple flower development, the predictable biennial bearing pattern of ‘Sciros’ was utilized (Bertelsen and Tustin, 2002). Low flowering and reduced cropping in ‘Off’ years results from the lack of floral induction on fruit-bearing trees in ‘On’ years and is accompanied by differential expression of several flowering regulator genes (Guitton et al, 2016). MdDAM genes in this study showed similar patterns regardless of fruit load, suggesting that DAM gene expression was not principally affected by the physiological states of apical buds.…”

Genome-wide identification of the 14-3-3 gene family and its participation in response to floral transition by interacting with TFL1/FT in Apple

“…Besides, similar nine trees were sprayed with water as a control. Next we collect the terminal buds of the short shoots (< 5cm) [69]. For each time point, three independent biological repeats with three technical repeats were performed.…”