The Tomato Hybrid Proline-rich Protein regulates the abscission zone competence to respond to ethylene signals

Abstract

The Tomato Hybrid Proline-rich Protein (THyPRP) gene was specifically expressed in the tomato (Solanum lycopersicum) flower abscission zone (FAZ), and its stable antisense silencing under the control of an abscission zone (AZ)-specific promoter, Tomato Abscission Polygalacturonase4, significantly inhibited tomato pedicel abscission following flower removal. For understanding the THyPRP role in regulating pedicel abscission, a transcriptomic analysis of the FAZ of THyPRP-silenced plants was performed, using a newly developed AZ-specific tomato microarray chip. Decreased expression of THyPRP in the silenced plants was already observed before abscission induction, resulting in FAZ-specific altered gene expression of transcription factors, epigenetic modifiers, post-translational regulators, and transporters. Our data demonstrate that the effect of THyPRP silencing on pedicel abscission was not mediated by its effect on auxin balance, but by decreased ethylene biosynthesis and response. Additionally, THyPRP silencing revealed new players, which were demonstrated for the first time to be involved in regulating pedicel abscission processes. These include: gibberellin perception, Ca2+-Calmodulin signaling, Serpins and Small Ubiquitin-related Modifier proteins involved in post-translational modifications, Synthaxin and SNARE-like proteins, which participate in exocytosis, a process necessary for cell separation. These changes, occurring in the silenced plants early after flower removal, inhibited and/or delayed the acquisition of the competence of the FAZ cells to respond to ethylene signaling. Our results suggest that THyPRP acts as a master regulator of flower abscission in tomato, predominantly by playing a role in the regulation of the FAZ cell competence to respond to ethylene signals.

Hydrogen sulfide inhibits ethylene-induced petiole abscission in tomato (Solanum lycopersicum L.)

“…Thereafter, through the perception of environmental and developmental signals, AZ cells attain the competence to respond to abscission signals (step 2) before the activation and execution of abscission (step 3) 1 . Finally, a protective layer is formed distal to the separation layers to protect the organs remaining on the plant from pathogen infection and water loss (step 4) [4][5][6] .…”

Role of the KNOTTED1-LIKE HOMEOBOX Protein (KD1) in regulating tomato flower pedicel abscission at early and late stages of the process

“…Therefore, we focused mainly on genes, which showed a modified expression in the FAZ before flower removal (zero time) and at 4 h after flower removal. This early period represents the timing in which the FAZ cells acquire the competence to respond to ethylene signals, which initiates the abscission process [1,2,7]. The next abscission phase, the execution stage, which starts during the period of 4 to 8 h after flower removal, can also be regulated both by signals derived from the previous stage, as well as by signals generated during this stage, that cannot be distinguished from one another.…”

“…The inflorescences of both WT and the KD1-antisense transgenic lines were harvested from 4-month-old plants as previously described [2,7]. The experiment protocols and pedicel abscission assays were performed in a controlled observation room maintained at 20°C and 60 to 70% relative humidity with continuous light of 14 μmol m -2 s -1 , as previously described [2,7,23]. The number of abscised pedicels was monitored daily by touching the distal side of the FAZ, for calculating the accumulated percentage of pedicel abscission.…”

“…For expression and microarray studies, we used samples of the FAZ and the NAZ of the WT and the FAZ of TAPG4::antisence KD1 line E, collected in duplicates at various time points (0, 4,8,12,16, and 20 h after flower removal). The RNA was extracted, treated with DNase, processed and checked for its quality, using the Agilent platform (Agilent, Palo Alto, CA), as previously described [7,22].…”

“…The experimental procedures for microarray labeling, hybridization, and scanning were performed as previously detailed [7], using the AZ-specific microarray chip, AMADID: 043310 (Genotypic Technology, Pvt. Ltd, Bangalore, India) for hybridization of the labeled cRNA samples [22].…”