Changes in transcription of cytokinin metabolism and signalling genes in grape (Vitis vinifera L.) berries are associated with the ripening-related increase in isopentenyladenine

Abstract

BackgroundCytokinins are known to play an important role in fruit set and early fruit growth, but their involvement in later stages of fruit development is less well understood. Recent reports of greatly increased cytokinin concentrations in the flesh of ripening kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang & A.R. Ferguson) and grapes (Vitis vinifera L.) have suggested that these hormones are implicated in the control of ripening-related processes.ResultsA similar pattern of isopentenyladenine (iP) accumulation was observed in the ripening fruit of several grapevine cultivars, strawberry (Fragaria ananassa Duch.) and tomato (Solanum lycopersicum Mill.), suggesting a common, ripening-related role for this cytokinin. Significant differences in maximal iP concentrations between grapevine cultivars and between fruit species might reflect varying degrees of relevance or functional adaptations of this hormone in the ripening process. Grapevine orthologues of five Arabidopsis (Arabidopsis thaliana L.) gene families involved in cytokinin metabolism and signalling were identified and analysed for their expression in developing grape berries and a range of other grapevine tissues. Members of each gene family were characterised by distinct expression profiles during berry development and in different grapevine organs, suggesting a complex regulation of cellular cytokinin activities throughout the plant. The post-veraison-specific expression of a set of biosynthesis, activation, perception and signalling genes together with a lack of expression of degradation-related genes during the ripening phase were indicative of a local control of berry iP concentrations leading to the observed accumulation of iP in ripening grapes.ConclusionsThe transcriptional analysis of grapevine genes involved in cytokinin production, degradation and response has provided a possible explanation for the ripening-associated accumulation of iP in grapes and other fruit. The pre- and post-veraison-specific expression of different members from each of five gene families suggests a highly complex and finely-tuned regulation of cytokinin concentrations and response to different cytokinin species at particular stages of fruit development. The same complexity and specialisation is also reflected in the distinct expression profiles of cytokinin-related genes in other grapevine organs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0611-5) contains supplementary material, which is available to authorized users.

Peduncle-girdling of Shiraz (Vitis viniferaL.) bunches and sugar concentration at the time of girdling affect wine volatile compounds

“…The physiological function of the post-veraison accumulation of iP reported previously (Böttcher et al 2013a(Böttcher et al , 2015a and also observed in this study (Figure 4a) is unknown, but might be related to the expansion-driven growth of ripening grapes and the establishment of berries as strong sink organs (Böttcher et al 2015a). The physiological function of the post-veraison accumulation of iP reported previously (Böttcher et al 2013a(Böttcher et al , 2015a and also observed in this study (Figure 4a) is unknown, but might be related to the expansion-driven growth of ripening grapes and the establishment of berries as strong sink organs (Böttcher et al 2015a).…”

“…Considering the significant reduction in Girdle 1 berry mass (Figure 1a), the increase in tZ concentration in girdling-affected berries could have been the result of berry shrinkage, but since tZ, in the form of its ribosides and ribotides, is mainly transported through the xylem (Hirose et al 2008), tZ import into berries was also conceivable. The only exception was the cytokinin activation gene VviLOG5a, which was linked to the post-veraison increase in iP concentration in a previous study [ Figure 4c (Böttcher et al 2015a)]. Enzymatic reactions were unlikely to be involved since genes related to cytokinin biosynthesis, degradation and iP to tZ conversion (Böttcher et al 2015a) were either unresponsive to girdling or were not expressed at a detectable level in the tested berry tissue.…”

“…The following plant hormones were extracted from powdered berry tissue (100 mg) and quantified with previously published LC-ESI-MS/MS methods: indole-3-acetic acid (IAA) and IAA-aspartic acid (IAA-Asp) (Böttcher et al 2011(Böttcher et al , 2012b, trans-zeatin (tZ) and N 6 -(Δ 2 -isopentenyl)-adenine (iP) (Böttcher et al 2015a), abscisic acid (ABA) and selected ABA metabolites (Speirs et al 2013). …”

“…Conversely, a small increase in the concentration of tZ was found over time in Girdle 1 and Control berries (Figure 4b). Enzymatic reactions were unlikely to be involved since genes related to cytokinin biosynthesis, degradation and iP to tZ conversion (Böttcher et al 2015a) were either unresponsive to girdling or were not expressed at a detectable level in the tested berry tissue. The reduced tZ concentration in Girdle 1 berries, however, compared with that of control berries, at 21 and 29 dpg in addition to the stagnating iP concentration in shrivelling Girdle 1 berries, were suggestive of girdlinginduced change to cytokinin metabolism.…”

“…Extraction of RNA, cDNA synthesis and quantitative real time polymerase chain reaction Böttcher et al (2013b) have previously described the extraction of RNA, cDNA synthesis and quantitative real time polymerase chain reaction (qRT-PCR), which have been modified by Böttcher et al (2015b). The gene-specific primers and the corresponding accession number for the following genes analysed in this study have been published previously: ACT2 (reference gene, Böttcher et al 2011); ethylene-related genes (Böttcher et al 2013c); ABA-related genes (Wheeler et al 2009); auxin-related genes (Böttcher et al 2011(Böttcher et al , 2013b; and cytokinin-related genes (Böttcher et al 2015a).…”