Abstract
BackgroundMature-fruit abscission (MFA) in fleshy-fruit is a genetically controlled process with mechanisms that, contrary to immature-fruit abscission, has not been fully characterized. Here, we use pyrosequencing to characterize the transcriptomes of melon abscission zone (AZ) at three stages during AZ-cell separation in order to understand MFA control at an early stage of AZ-activation.Principal FindingsThe results show that by early induction of MFA, the melon AZ exhibits major gene induction, while by late induction of MFA, melon AZ shows major gene repression. Although some genes displayed similar regulation in both early and late induction of abscission, such as EXT1-EXT4, EGase1, IAA2, ERF1, AP2D15, FLC, MADS2, ERAF17, SAP5 and SCL13 genes, the majority had different expression patterns. This implies that time-specific events occur during MFA, and emphasizes the value of characterizing multiple time-specific abscission transcriptomes. Analysis of gene-expression from these AZs reveal that a sequential induction of cell-wall-degrading genes is associated with the upregulation of genes involved in endo and exocytosis, and a shift in plant-hormone metabolism and signaling genes during MFA. This is accompanied by transcriptional activity of small-GTPases and synthaxins together with tubulins, dynamins, V-type ATPases and kinesin-like proteins potentially involved in MFA signaling. Early events are potentially controlled by down-regulation of MADS-box, AP2/ERF and Aux/IAA transcription-factors, and up-regulation of homeobox, zinc finger, bZIP, and WRKY transcription-factors, while late events may be controlled by up-regulation of MYB transcription-factors.SignificanceOverall, the data provide a comprehensive view on MFA in fleshy-fruit, identifying candidate genes and pathways associated with early induction of MFA. Our comprehensive gene-expression profile will be very useful for elucidating gene regulatory networks of the MFA in fleshy-fruit.
Highlights
Melon (Cucumis melo L.), an important crop worldwide and an annual diploid plant, has a high intra-specific genetic variation and a small genome size (454 Mb), which can be exploited to dissect biological processes of great technological importance, among them flavour development and textural changes that occur during fruit ripening [1,2]
By studying the segregation of the activation of the abscission zone (AZ) and ethylene production on a population of recombinant cantaloupe Charentais 6 PI 161375 inbred lines, we have previously demonstrated that both the mature-fruit abscission (MFA) and climacteric characters were controlled by two duplicated independent loci (Al-3 and Al-4) and that the intensity of ethylene production was controlled by at least four quantitative trait loci (QTLs) localized in other genomic regions [16]
The AZ was characterized in Vedrantais melon fruit by scanning electron microscopy (SEM) at 30, 36, 38, and 40 days post-anthesis (DPA), comprising 30– 35 cell layers (Fig. 1D, 1H, 1I, 1J)
Summary
Melon (Cucumis melo L.), an important crop worldwide and an annual diploid plant, has a high intra-specific genetic variation and a small genome size (454 Mb), which can be exploited to dissect biological processes of great technological importance, among them flavour development and textural changes that occur during fruit ripening [1,2]. Analysis of our current data set confirms the abscission-induced accumulation of transcripts putatively involved in changing cell-wall composition and properties, including 79 differentially expressed genes that encode proteins with probable functions in cell-wall remodeling during melon MFA (Fig. 3; Tables S8, S9).
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