Suppression of a Prolyl 4 Hydroxylase Results in Delayed Abscission of Overripe Tomato Fruits.

Andreas Perrakis,Khansa Mekkaoui,Dusan Denic,Konstantinos N Blazakis,Afrodite Krokida,Dimitrios Kaloudas,Craita E Bita,Panagiotis Kalaitzis,Stilianos Arhondakis

doi:10.3389/fpls.2019.00348

Andreas Perrakis, Khansa Mekkaoui + Show 7 more

Open Access

https://doi.org/10.3389/fpls.2019.00348

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Abstract

The tomato pedicel abscission zone (AZ) is considered a model system for flower and fruit abscission development, activation, and progression. O-glycosylated proteins such as the Arabidopsis IDA (INFLORESCENCE DEFICIENT IN ABSCISSION) peptide and Arabinogalactan proteins (AGPs) which undergo proline hydroxylation were demonstrated to participate in abscission regulation. Considering that the frequency of occurrence of proline hydroxylation might determine the structure as well the function of such proteins, the expression of a tomato prolyl 4 hydroxylase, SlP4H3 (Solanum lycopersicum Prolyl 4 Hydroxylase 3) was suppressed in order to investigate the physiological significance of this post-translational modification in tomato abscission. Silencing of SlP4H3 resulted in the delay of abscission progression in overripe tomato fruits 90 days after the breaker stage. The cause of this delay was attributed to the downregulation of the expression of cell wall hydrolases such as SlTAPGs (tomato abscission polygalacturonases) and cellulases as well as expansins. In addition, minor changes were observed in the mRNA levels of two SlAGPs and one extensin. Moreover, structural changes were observed in the silenced SlP4H3AZs. The fracture plane of the AZ was curved and not along a line as in wild type and there was a lack of lignin deposition in the AZs of overripe fruits 30 days after breaker. These results suggest that proline hydroxylation might play a role in the regulation of tomato pedicel abscission.

Highlights

Abscission is the process of organ separation in plants with significant implications in crop productivity considering that fruit and flower abscission might affect yield in several crops (Addicott, 1982; Tranbarger et al, 2017)
prolyl 4 hydroxylases (P4Hs) catalyze the post-translational modification of proline hydroxylation in HRGPs such as Arabinogalactan proteins (AGPs) and extensins as well as in hormone peptides such as the Arabidopsis IDA and CLAVATA3 (Matsubayashi, 2014)
With regard to AGPs, it was observed that Arabinogalactan was secreted in the abscission zone (AZ) of Arabidopsis flowers after staining with the β-Yariv reagent which is known to bind AGPs (Stenvik et al, 2006)

Summary

Introduction

Abscission is the process of organ separation in plants with significant implications in crop productivity considering that fruit and flower abscission might affect yield in several crops (Addicott, 1982; Tranbarger et al, 2017). Some plant species such as Arabidopsis and tomato are considered model systems for abscission studies, Arabidopsis for flower abscission and tomato for pedicel abscission. The tomato pedicel comprises a distinct AZ at a predetermined position which is responsible for the detachment of either the flower or the fruit when the abscission process initiates This AZ is comprised of six to eight cell layers at the open flower stage. SlEXP1 and SlEXP11 were shown to be upregulated in flower AZs after 6 h of ethylene treatment (Wang et al, 2013)

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