The α-Crystallin Domain Containing Genes: Identification, Phylogeny and Expression Profiling in Abiotic Stress, Phytohormone Response and Development in Tomato (Solanum lycopersicum).

Asosii Paul,Saloni Mathur,Sombir Rao

doi:10.3389/fpls.2016.00426

Asosii Paul, Saloni Mathur + Show 1 more

Open Access

https://doi.org/10.3389/fpls.2016.00426

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Abstract

The α-crystallin domain (ACD) is an ancient domain conserved among all kingdoms. Plant ACD proteins have roles in abiotic stresses, transcriptional regulation, inhibiting virus movement, and DNA demethylation. An exhaustive in-silico analysis using Hidden Markov Model-based conserved motif search of the tomato proteome yielded a total of 50 ACD proteins that belonged to four groups, sub-divided further into 18 classes. One of these groups belongs to the small heat shock protein (sHSP) class of proteins, molecular chaperones implicated in heat tolerance. Both tandem and segmental duplication events appear to have shaped the expansion of this gene family with purifying selection being the primary driving force for evolution. The expression profiling of the Acd genes in two different heat stress regimes suggested that their transcripts are differentially regulated with roles in acclimation and adaptive response during recovery. The co-expression of various genes in response to different abiotic stresses (heat, low temperature, dehydration, salinity, and oxidative stress) and phytohormones (abscisic acid and salicylic acid) suggested possible cross-talk between various members to combat a myriad of stresses. Further, several genes were highly expressed in fruit, root, and flower tissues as compared to leaf signifying their importance in plant development too. Evaluation of the expression of this gene family in field grown tissues highlighted the prominent role they have in providing thermo-tolerance during daily temperature variations. The function of three putative sHSPs was established as holdase chaperones as evidenced by protection to malate-dehydrogenase against heat induced protein-aggregation. This study provides insights into the characterization of the Acd genes in tomato and forms the basis for further functional validation in-planta.

Highlights

The α-crystallin domain (ACD) is an evolutionarily conserved domain from archaea to eukaryotes (Bondino et al, 2012)
Fifty putative ACD proteins were identified (Table 1) in tomato that were further confirmed for the presence of the ACD in conserved domain database (CDD) database at National Center for Biotechnology Information (NCBI) (Supplementary Table 2)
The domain of unknown function (DUF966) and 2Fe-2S iron-sulfur cluster binding (Fer2) domain involved in electron transfer processes and various enzymatic reactions are found in SlAcd26.8-CVII and SlAcd32.3-CIX, respectively (Supplementary Table 2)

Summary

Introduction

The α-crystallin domain (ACD) is an evolutionarily conserved domain from archaea to eukaryotes (Bondino et al, 2012). The name ACD is derived from the eye lens α-crystallin protein, a chaperone preventing non-native or denatured proteins from aggregation and preventing cataracts in vertebrates (Horwitz, 1992). This domain comprises of two conserved regions that form a sandwich of two pleated β-sheets separated by a hydrophilic domain of variable length. The small heat shock proteins (sHSPs) group, the transcription factor (TF) group, sodiumlithium (NaLi) group, and the uncharacterized ACD proteins (UAP) group (Bondino et al, 2012). The sHSPs have been reported to regulate the activity heat shock factors (Hsfs) by influencing the transcriptional activity, solubility and intracellular distribution of Hsfs to modulate thermo-tolerance during heat stress (Scharf et al, 1998; Port et al, 2004)

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