Expression profiling of tomato pre-abscission pedicels provides insights into abscission zone properties including competence to respond to abscission signals

Abstract

BackgroundDetachment of plant organs occurs in abscission zones (AZs). During plant growth, the AZ forms, but does not develop further until the cells perceive abscission-promoting signals and initiate detachment. Upon signal perception, abscission initiates immediately; if there is no signal, abscission is not induced and the organ remains attached to the plant. However, little attention has been paid to the genes that maintain competence to respond to the abscission signal in the pre-abscission AZ. Recently, we found that the tomato (Solanum lycopersicum) transcription factors BLIND (Bl), GOBLET (GOB), Lateral suppressor (Ls) and a tomato WUSCHEL homologue (LeWUS) are expressed specifically in pre-abscission tissue, the anthesis pedicel AZs. To advance our understanding of abscission, here we profiled genome-wide gene expression in tomato flower pedicels at the pre-abscission stage.ResultsWe examined the transcriptomes of three tomato flower pedicel regions, the AZ and flanking proximal- (Prox) and distal- (Dis) regions, and identified 89 genes that were preferentially expressed in the AZ compared to both Prox and Dis. These genes included several transcription factors that regulate apical or axillary shoot meristem activity. Also, genes associated with auxin activity were regulated in a Prox-Dis region-specific manner, suggesting that a gradient of auxin exists in the pedicel. A MADS-box gene affecting floral transition was preferentially expressed in the Prox region and other MADS-box genes for floral organ identification were preferentially expressed in Dis, implying that the morphologically similar Prox and Dis regions have distinct identities. We also analyzed the expression of known regulators; in anthesis pedicels, Bl, GOB, Ls and LeWUS were expressed in the vascular cells of the AZ region. However, after an abscission signal, Bl was up-regulated, but GOB, Ls and LeWUS were down-regulated, suggesting that Bl may be a positive regulator of abscission, but the others may be negative regulators.ConclusionsThis study reveals region-specific gene expression in tomato flower pedicels at anthesis and identifies factors that may determine the physiological properties of the pre-abscission pedicel. The region-specific transcriptional regulators and genes for auxin activity identified here may prevent flower abscission in the absence of signal or establish competence to respond to the abscission signal.

Ethylene-dependent effects on generative organ abscission of Lupinus luteus

“…The increasing expression of the genes coding for ET biosynthesis enzymes, the increase in the ACC content, as well as studies of ACC immunolocalization in the abscission zone, all suggest that ethylene is directly involved in the functioning of the flower abscission zone in L. luteus. This hypothesis was also confirmed by the results of research performed in other plant species, in which the factors activating abscission of particular organs stimulate the expression of both ACC synthases and oxidases, e.g., in apple (MdACO3, MdACO4, MdACO1) or tomato (SlACO5, LACS2) [41][42][43][44]. Moreover, it was found that immediately before flower abscission in Ecballium elaterum and S. lycopersicum [45,46], the ethylene production rate increases.…”

Additional Amphivasal Bundles in Pedicel Pith Exacerbate Central Fruit Dominance and Induce Self-Thinning of Lateral Fruitlets in Apple

“…These include homologs of AT2G43890, AT3G07970 (Fig. 9), and AT3G59850, which were previously found overexpressed in Arabidopsis and tomato pedicel AZs (Kim and Patterson, 2006;González-Carranza et al, 2007;Nakano et al, 2013). In parallel with the expression of cell wallmodifying enzymes, we also identified several genes associated with senescence, response to dehydration, and desiccation (Table III), which is consistent with pedicel drop.…”

“…We found that genes involved in the stress response were largely induced in L1 pedicels, indicating an activation of protection systems during abscission. The expression of chitinase B1 (CHIB1) and allergen family proteins in the AZ had previously been reported in tomato (Nakano et al, 2013) and Sambucus nigra (Ruperti et al, 1999), respectively. Consistent with the observed fruit growth arrest, genes involved in sugar synthesis and transport were also down-regulated in L1 pedicels throughout the three phases investigated.…”

KNOX Protein OSH15 Induces Grain Shattering by Repressing Lignin Biosynthesis Genes

“…This set of cellular characteristics is reminiscent of meristematic tissues. Several genes involved in SAM maintenance and the initiation of axillary meristems are expressed in the AZ (Shi et al, 2011;Nakano et al, 2013;Wang et al, 2013). Therefore, it has been proposed that AZ cells have a meristematic identity.…”