Transcriptome Analysis of Tomato Flower Pedicel Tissues Reveals Abscission Zone-Specific Modulation of Key Meristem Activity Genes

Xiang Wang,Xiuli Sun,Yanchun Liang,Long Mao,Danmei Liu,Aili Li,Rongzhi Zhang,Liang Wu,Tobias Isaac Baskin

doi:10.1371/journal.pone.0055238

Abstract

Tomato flower abscises at the anatomically distinct abscission zone that separates the pedicel into basal and apical portions. During abscission, cell separation occurs only at the abscission zone indicating distinctive molecular regulation in its cells. We conducted a transcriptome analysis of tomato pedicel tissues during ethylene promoted abscission. We found that the abscission zone was the most active site with the largest set of differentially expressed genes when compared with basal and apical portions. Gene Ontology analyses revealed enriched transcription regulation and hydrolase activities in the abscission zone. We also demonstrate coordinated responses of hormone and cell wall related genes. Besides, a number of ESTs representing homologs of key Arabidopsis shoot apical meristem activity genes were found to be preferentially expressed in the abscission zone, including WUSCHEL (WUS), KNAT6, LATERAL ORGAN BOUNDARIES DOMAIN PROTEIN 1(LBD1), and BELL-like homeodomain protein 1 (BLH1), as well as tomato axillary meristem genes BLIND (Bl) and LATERAL SUPPRESSOR (Ls). More interestingly, the homologs of WUS and the potential functional partner OVATE FAMILIY PROTEIN (OFP) were subsequently down regulated during abscission while Bl and AGL12 were continuously and specifically induced in the abscission zone. The expression patterns of meristem activity genes corroborate the idea that cells of the abscission zone confer meristem-like nature and coincide with the course of abscission and post-abscission cell differentiation. Our data therefore propose a possible regulatory scheme in tomato involving meristem genes that may be required not only for the abscission zone development, but also for abscission.

Highlights

Organ abscission is a ubiquitous physiological process in the plant kingdom
A vast number of genes, hydrolytic enzymes, such as polygalacturonases (PGs), xyloglucan endotransglucosylase/hydrolase (XTH), b-1,4-glucanase, and expansins have been shown to be implicated in abscission for the degradation of cell wall and middle lamella at the abscission zones that eventually result in the shedding of distal organs [1], [2], [3], [4], [5], [6]
Other genes contributing to the abscission zone development and its capacity are transcription factors (TFs) including MADS-box genes AGL15 and AGL18 [11], KNAT/Biological Process (BP) [12], and AtZFP2 (ZINC FINGER PROTEIN2) [13]

Summary

Introduction

Organ abscission is a ubiquitous physiological process in the plant kingdom. While seasonal senescence and foliage abscission set the enchanted autumn scenery, the dispersal of seeds and the efficiency of grain threshing and fruit picking are highly relevant to agriculture. A vast number of genes, hydrolytic enzymes, such as polygalacturonases (PGs), xyloglucan endotransglucosylase/hydrolase (XTH), b-1,4-glucanase (cellulase), and expansins have been shown to be implicated in abscission for the degradation of cell wall and middle lamella at the abscission zones that eventually result in the shedding of distal organs [1], [2], [3], [4], [5], [6] During this process, ethylene is known to be an efficient accelerator for organ abscission, the initiation of abscission is considered to be timed or repressed by auxin [6], [7], [8], [9]. An intrinsic relation between the development of the abscission zone and its function is plausible

Methods

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Conclusion