Abstract
Heat shock protein 70 (Hsp70) plays an essential role in plant growth and development, as well as stress response. Rapeseed (Brassica napus L.) originated from recently interspecific hybridization between Brassica rapa and Brassica oleracea. In this study, a total of 47 Hsp70 genes were identified in B. napus (AnAnCnCn genome), including 22 genes from An subgenome and 25 genes from Cn subgenome. Meanwhile, 29 and 20 Hsp70 genes were explored in B. rapa (ArAr genome) and B. oleracea (CoCo genome), respectively. Based on phylogenetic analysis, 114 Hsp70 proteins derived from B. napus, B. rapa, B. oleracea and Arabidopsis thaliana, were divided into 6 subfamilies containing 16 Ar-An and 11 Co-Cn reliable orthologous pairs. The homology and synteny analysis indicated whole genome triplication and segmental duplication may be the major contributor for the expansion of Hsp70 gene family. Intron gain of BnHsp70 genes and domain loss of BnHsp70 proteins also were found in B. napus, associating with intron evolution and module evolution of proteins after allopolyploidization. In addition, transcriptional profiles analyses indicated that expression patterns of most BnHsp70 genes were tissue-specific. Moreover, Hsp70 orthologs exhibited different expression patterns in the same tissue and Cn subgenome biased expression was observed in leaf. These findings contribute to exploration of the evolutionary adaptation of polyploidy and will facilitate further application of BnHsp70 gene functions.
Highlights
Taken as a whole, polyploidization has long been seen as a key force in the evolution of eukaryotic nuclear genomes, and about 70% of angiosperms have experienced relatively recent genome doubling in the form of polyploidy (Masterson, 1994)
To systematically explore all of the Heat shock protein 70 (Hsp70) gene family members, 107, 39 and 33 nonredundant putative protein sequences of B. napus, B. rapa and B. oleracea were initially retrieved by BLASTn program in Brassica database (BRAD)
A total of 61, 11 and 22 sequences of B. napus, B. rapa and B. oleracea were discarded for lack of Hsp70-specific function domain
Summary
Polyploidization has long been seen as a key force in the evolution of eukaryotic nuclear genomes, and about 70% of angiosperms have experienced relatively recent genome doubling in the form of polyploidy (Masterson, 1994). The onset of genomic shock occurred accompanied by the merger of two distinct genomes reunited in a common nucleus (McClintock, 1984). This collision among the subgenomes sometimes leads to subgenome bias and even to the dominance of one of a subgenome, affecting homologous exchanges, epigenetic regulation and gene expression (Bird et al, 2018). Recent insights into subgenome bias and duplicate gene retention in polyploids contribute to sharpen researches of polyploid adaptation and provide great opportunities for trait improvement of polyploid species in agriculture (Samans, Chalhoub & Snowdon, 2017; Bird et al, 2018)
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