Multiple evidence for the role of an Ovate-like gene in determining fruit shape in pepper

Aphrodite Tsaballa,Athanasios S Tsaftaris,Konstantinos Pasentsis,Nikos Darzentas

doi:10.1186/1471-2229-11-46

Aphrodite Tsaballa, Athanasios S Tsaftaris + Show 2 more

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https://doi.org/10.1186/1471-2229-11-46

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Abstract

BackgroundGrafting is a widely used technique contributing to sustainable and ecological production of many vegetables, but important fruit quality characters such as taste, aroma, texture and shape are known for years to be affected by grafting in important vegetables species including pepper. From all the characters affected, fruit shape is the most easily observed and measured. From research in tomato, fruit shape is known to be controlled by many QTLs but only few of them have larger effect on fruit shape variance. In this study we used pepper cultivars with different fruit shape to study the role of a pepper Ovate-like gene, CaOvate, which encodes a negative regulator protein that brings significant changes in tomato fruit shape.ResultsWe successfully cloned and characterized Ovate-like genes (designated as CaOvate) from two pepper cultivars of different fruit shape, cv. "Mytilini Round" and cv. "Piperaki Long", hereafter referred to as cv. "Round" and cv. "Long" after the shape of their mature fruits. The CaOvate consensus contains a 1008-bp ORF, encodes a 335 amino-acid polypeptide, shares 63% identity with the tomato OVATE protein and exhibits high similarity with OVATE sequences from other Solanaceae species, all placed in the same protein subfamily as outlined by expert sequence analysis. No significant structural differences were detected between the CaOvate genes obtained from the two cultivars. However, relative quantitative expression analysis showed that the expression of CaOvate followed a different developmental profile between the two cultivars, being higher in cv. "Round". Furthermore, down-regulation of CaOvate through VIGS in cv. "Round" changes its fruit to a more oblong form indicating that CaOvate is indeed involved in determining fruit shape in pepper, perhaps by negatively affecting the expression of its target gene, CaGA20ox1, also studied in this work.ConclusionsHerein, we clone, characterize and study CaOvate and CaGA20ox1 genes, very likely involved in shaping pepper fruit. The oblong phenotype of the fruits in a plant of cv. "Round", where we observed a significant reduction in the expression levels of CaOvate, resembled the change in shape that takes place by grafting the round-fruited cultivar cv. "Round" onto the long-fruited pepper cultivar cv. "Long". Understanding the role of CaOvate and CaGA20ox1, as well as of other genes like Sun also involved in controlling fruit shape in Solanaceae plants like tomato, pave the way to better understand the molecular mechanisms involved in controlling fruit shape in Solanaceae plants in general, and pepper in particular, as well as the changes in fruit quality induced after grafting and perhaps the ways to mitigate them.

Highlights

Grafting is a widely used technique contributing to sustainable and ecological production of many vegetables, but important fruit quality characters such as taste, aroma, texture and shape are known for years to be affected by grafting in important vegetables species including pepper
Recent studies in Arabidopsis implicated a second member of the OVATE Family of Proteins (OFPs), AtOFP1, to the regulation of cell elongation, by suppressing AtGA20ox1, a gene that encodes a critical enzyme in the gibberilin (GA) pathway [4]
Cloning of CaOvate A 3’ RACE approach was used along with an Ovate gene-specific primer, OVATE FOR 1, designed on a specific region identified by BLAST, of a C. frutescens BAC clone genomic sequence to obtain a full-length CaOvate cDNA

Summary

Introduction

Grafting is a widely used technique contributing to sustainable and ecological production of many vegetables, but important fruit quality characters such as taste, aroma, texture and shape are known for years to be affected by grafting in important vegetables species including pepper. In tomato (S. lycopersicum) fruit shape is controlled by many Quantitative Trait Loci (QTLs) but only few of them attribute mostly to variance: Ovate, Sun, Fruit Shape (Fs) 8.1 and Triangle (Tri) 2.1/Blockiness (Dblk) 2.1 [1] The first of these loci, Ovate, is a major QTL that as was shown first in tomato, encodes a negative regulator of fruit elongation protein, acting early in flower and fruit development [2]. KNOX and BELL homeodomain proteins belong to the TALE (Three-Amino-acid Loop Extension) protein superfamily and they interact [10,11,12,13,14] forming heterodimers The action of such a BELL-KNOX heterodimer was shown to be negatively regulated by AtOFP5 ensuring normal embryo sac growth in Arabidopsis [15]. Potato TALE proteins, StBEL5 and POTH1, were shown to interact and bind to a specific 10-bp sequence of the promoter of GA20ox1 [16]

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