Abstract
BackgroundGibberellins (GA3) are the most sprayed growth regulator for table grape production worldwide, increasing berry size of seedless varieties through pericarp cell expansion. However, these treatments also exacerbate berry drop, which has a detrimental effect on the postharvest quality of commercialized clusters. Several studies have suggested that pedicel stiffening caused by GA3 would have a role in this disorder. Nevertheless, transcriptional and phenotypic information regarding pedicel responses to GA3 is minimal.ResultsCharacterization of responses to GA3 treatments using the lines L23 and Thompson Seedless showed that the former was up to six times more susceptible to berry drop than the latter. GA3 also increased the diameter and dry matter percentage of the pedicel on both genotypes. Induction of lignin biosynthesis-related genes by GA3 has been reported, so the quantity of this polymer was measured. The acetyl bromide method detected a decreased concentration of lignin 7 days after GA3 treatment, due to a higher cell wall yield of the isolated fractions of GA3-treated pedicel samples which caused a dilution effect. Thus, an initial enrichment of primary cell wall components in response to GA3 was suggested, particularly in the L23 background. A transcriptomic profiling was performed to identify which genes were associated with these phenotypic changes. This analysis identified 1281 and 1787 genes differentially upregulated by GA3 in L23 and cv. Thompson Seedless, respectively. Concomitantly, 1202 and 1317 downregulated genes were detected in L23 and cv. Thompson Seedless (FDR < 0.05). Gene ontology analysis of upregulated genes showed enrichment in pathways including phenylpropanoids, cell wall metabolism, xylem development, photosynthesis and the cell cycle at 7 days post GA3 application. Twelve genes were characterized by qPCR and striking differences were observed between genotypes, mainly in genes related to cell wall synthesis.ConclusionsHigh levels of berry drop are related to an early strong response of primary cell wall synthesis in the pedicel promoted by GA3 treatment. Genetic backgrounds can produce similar phenotypic responses to GA3, although there is considerable variation in the regulation of genes in terms of which are expressed, and the extent of transcript levels achieved within the same time frame.
Highlights
Gibberellins (GA3) are the most sprayed growth regulator for table grape production worldwide, increasing berry size of seedless varieties through pericarp cell expansion
Thompson seedless under gibberellic acid-3 (GA3) treatment conditions To compare the differential response of L23 and cv
Lignin concentration reached similar values for both treated and untreated groups at advanced stages such as harvest time; (iii) transcriptome profiling of samples after treatment provided cues on the main biological processes upregulated by GA3, which can be summarized as promotion of vegetative growth through positive regulation of cell growth, cell wall modification, xylem development, phenylpropanoid and flavonoid metabolism, along with downregulation of stress-related responses; and (iv) core responses are similar between the genotypes, one more tolerant and one more susceptible to postharvest berry drop, there are a number of differentially expressed genes (DEGs) that are specific to each one
Summary
Gibberellins (GA3) are the most sprayed growth regulator for table grape production worldwide, increasing berry size of seedless varieties through pericarp cell expansion. These treatments exacerbate berry drop, which has a detrimental effect on the postharvest quality of commercialized clusters. The exogenous application of gibberellic acid-3 (GA3) during key phases of fruit development is critical for seedless grape varieties, since it promotes berry enlargement through elongation of pericarp cells [1, 2] These treatments are beneficial in terms of meeting the market standards at expected fruit caliber, they exacerbate berry drop ( known as shattering) during postharvest [3]. There are varieties such as cv: Thompson Seedless which can be considered as non-sensitive to berry drop as long as proper management conditions are achieved: with only three GA doses applied for berry size enlargement spanning at specific fruit developmental stages [4, 6]
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