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.
Highlights
Detachment of plant organs occurs in abscission zones (AZs)
In tomato (Solanum lycopersicum), “jointless” cultivars with mutations inhibiting pedicel AZ development have been widely adopted for mechanical harvesting, because in the absence of an AZ, the stem and sepals remain on the plant, allowing the fruit to be harvested without the green tissues
Comparative transcriptome analysis revealed genes upregulated in the AZ of tomato flower pedicels at anthesis AZ cells of a tomato flower are recognized even at the early stage of flower primordium development; at the flower anthesis stage, six to eight layers of cells are observed in the AZ and the flower pedicels have acquired the competence to respond to abscission-promoting signals [27,33,34]
Summary
Detachment of plant organs occurs in abscission zones (AZs). The AZ forms, but does not develop further until the cells perceive abscission-promoting signals and initiate detachment. Plants can detach aged leaves, unfertilized flowers, diseased or damaged organs and mature fruits or ripe seeds. These abscission processes enable plants to recycle nutrients for continuous growth, develop appropriate organs, survive diseases, and facilitate reproduction [1,2]. In tomato (Solanum lycopersicum), “jointless” cultivars with mutations inhibiting pedicel AZ development have been widely adopted for mechanical harvesting, because in the absence of an AZ, the stem and sepals remain on the plant, allowing the fruit to be harvested without the green tissues
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