Abstract
Sesame is a survivor crop cultivated for ages in arid areas under high temperatures and limited water conditions. Since its entire genome has been sequenced, revealing evolution, and functional characterization of its abiotic stress genes became a hot topic. In this study, we performed a whole-genome identification and analysis of Hsf gene family in sesame. Thirty genes encoding Hsf domain were found and classified into 3 major classes A, B, and C. The class A members were the most representative one and Hsf genes were distributed in 12 of the 16 linkage groups (except the LG 8, 9, 13, and 16). Evolutionary analysis revealed that, segmental duplication events which occurred around 67 MYA, were the primary force underlying Hsf genes expansion in sesame. Comparative analysis also suggested that sesame has retained most of its Hsf genes while its relatives viz. tomato and potato underwent extensive gene losses during evolution. Continuous purifying selection has played a key role in the maintenance of Hsf genes in sesame. Expression analysis of the Hsf genes in sesame revealed their putative involvement in multiple tissue-/developmental stages. Time-course expression profiling of Hsf genes in response to drought stress showed that 90% Hsfs are drought responsive. We infer that classes B-Hsfs might be the primary regulators of drought response in sesame by cooperating with some class A genes. This is the first insight into this gene family and the results provide some gene resources for future gene cloning and functional studies toward the improvement in stress tolerance of sesame.
Highlights
To cope with environmental stresses, plants have developed complex transcriptional systems that involve transcription factors (Mittler, 2006)
Based on the genome and proteome sequences of sesame downloaded from the Sinbase (Wang et al, 2014), an extensive search was performed to identify all members of the heat shock transcription factors (Hsfs) gene family
A total of 30 Hsf genes were confirmed in sesame genome with apparently complete Hsf-type DNA-binding domains and oligomerization domains ranging from 255 to 2646 bp in length (Table 1, Supplementary Table 2)
Summary
To cope with environmental stresses, plants have developed complex transcriptional systems that involve transcription factors (Mittler, 2006). Transcription Factors (TFs) are important for regulating gene expression in responses to biotic or abiotic stimuli. Hsfs constitute an important gene family involved in plant growth and development, as well as in responses to abiotic stresses (von Koskull-Döring et al, 2007). Hsf genes are released from chaperone complexes, recognize the conserved binding motifs (heat shock elements, HSEs) within the promoters of Hsf-responsive genes (Bienz and Pelham, 1987) and undergo phosphorylation, sumoylation, trimerisation and nuclear import (Baniwal et al, 2004; Scharf et al, 2012). Class A Hsfs are involved in transcriptional activation and environmental stress responses (Shim et al, 2009), while Hsfs in class B lack the AHA activator domain and serve as repressors of gene expression (Ikeda et al, 2011) or trancriptional coactivators with class A Hsfs (Wang J. et al, 2014). There is no information regarding the functions of class C members
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