Abstract
The Hsp20 genes are involved in the response of plants to environment stresses including heat shock and also play a vital role in plant growth and development. They represent the most abundant small heat shock proteins (sHsps) in plants, but little is known about this family in tomato (Solanum lycopersicum), an important vegetable crop in the world. Here, we characterized heat shock protein 20 (SlHsp20) gene family in tomato through integration of gene structure, chromosome location, phylogenetic relationship, and expression profile. Using bioinformatics-based methods, we identified at least 42 putative SlHsp20 genes in tomato. Sequence analysis revealed that most of SlHsp20 genes possessed no intron or a relatively short intron in length. Chromosome mapping indicated that inter-arm and intra-chromosome duplication events contributed remarkably to the expansion of SlHsp20 genes. Phylogentic tree of Hsp20 genes from tomato and other plant species revealed that SlHsp20 genes were grouped into 13 subfamilies, indicating that these genes may have a common ancestor that generated diverse subfamilies prior to the mono-dicot split. In addition, expression analysis using RNA-seq in various tissues and developmental stages of cultivated tomato and the wild relative Solanum pimpinellifolium revealed that most of these genes (83%) were expressed in at least one stage from at least one genotype. Out of 42 genes, 4 genes were expressed constitutively in almost all the tissues analyzed, implying that these genes might have specific housekeeping function in tomato cell under normal growth conditions. Two SlHsp20 genes displayed differential expression levels between cultivated tomato and S. pimpinellifolium in vegetative (leaf and root) and reproductive organs (floral bud and flower), suggesting inter-species diversification for functional specialization during the process of domestication. Based on genome-wide microarray analysis, we showed that the transcript levels of SlHsp20 genes could be induced profusely by abiotic and biotic stresses such as heat, drought, salt, Botrytis cinerea, and Tomato Spotted Wilt Virus (TSWV), indicating their potential roles in mediating the response of tomato plants to environment stresses. In conclusion, these results provide valuable information for elucidating the evolutionary relationship of Hsp20 gene family and functional characterization of the SlHsp20 gene family in the future.
Highlights
Plants live in a complex environment, where multiple biotic and abiotic stresses may seriously restrict their growth and development (Cramer et al, 2011)
Name search and Hidden Markov Model (HMM) analysis showed a total of 42 candidate SlHsp20 genes, four of which were identified to contain incomplete Hsp20 domains
The SlHsp20 genes were named according to their molecular weight in our study
Summary
Plants live in a complex environment, where multiple biotic and abiotic stresses may seriously restrict their growth and development (Cramer et al, 2011). Due to unprecedented global warming caused by various factors, high temperature has appeared as one of the most severe abiotic stresses around the world. To survive and acclimatize under the adverse environment conditions, plants have established self-defense mechanisms during the course of long-term evolution. Previous studies have shown that high temperature as well as other environmental cues (cold, salinity, drought, heavy metals, anoxia, pathogens, etc.) could induce the occurrence of Hsps (Lindquist and Craig, 1988; Wang et al, 2003). The Hsps were found to be associated with plant growth and development, such as embryogenesis, seed germination, and fruit maturation (NetaSharir et al, 2005)
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