Abstract
Heat shock protein 20 (Hsp20) genes play important roles in plant growth, development, and response to environmental stress. However, the Hsp20 gene family has not yet been systematically investigated, and its function in red algae (Rhodophyta) remains poorly understood. Herein, we characterized Hsp20 gene families in red algae by studying gene structure, conserved motifs, phylogenetic relationships, chromosome location, gene duplication, cis-regulatory elements, and expression profiles. In this study, 97 Hsp20 genes were identified using bioinformatic methods and classified into 13 subfamilies based on phylogenetic relationships. Phylogenetic analysis revealed that Hsp20 genes might have a polyphyletic origin and a complex evolutionary pattern. Gene structure analysis revealed that most Hsp20 genes possessed no introns, and all Hsp20 genes contained a conserved α-crystalline domain in the C-terminal region. Conserved motif analysis revealed that Hsp20 genes belonging to the same subfamily shared similar motifs. Gene duplication analysis demonstrated that tandem and segmental duplication events occurred in these gene families. Additionally, these gene families in red algae might have experienced strong purifying selection pressure during evolution, and Hsp20 genes in Pyropia yezoensis, Pyropia haitanensis, and Porphyra umbilicalis were highly evolutionarily conserved. The cis-elements of phytohormone-, light-, stress-responsive, and development-related were identified in the red algal Hsp20 gene promoter sequences. Finally, using Py. yezoensis, as a representative of red algae, the Hsp20 gene expression profile was explored. Based on the RNA-seq data, Py. yezoensis Hsp20 (PyyHsp20) genes were found to be involved in Py. yezoensis responses against abiotic and biotic stresses and exhibited diverse expression patterns. Moreover, PyyHsp20 is involved in Py. yezoensis growth and development and revealed spatial and temporal expression patterns. These results provide comprehensive and valuable information on Hsp20 gene families in red algae and lay a foundation for their functional characterization. In addition, our study provides new insights into the evolution of Hsp20 gene families in red algae and will help understand the adaptability of red algae to diverse environments.
Highlights
In recent years, heat has become a prominent abiotic stress factor owing to global warming
Detailed information on the red algal Hsp20 genes is shown in Supplementary Table 4, including names, chromosome locations, intron numbers, protein lengths, molecular weights, pI values, and instability index
The prediction of the subcellular localization of red algal Hsp20s is shown in Supplementary Table 5
Summary
Heat has become a prominent abiotic stress factor owing to global warming. All organisms synthesize a set of proteins called heat shock proteins (HSPs) to combat heat stress (Lindquist and Craig, 1988). According to protein molecular weight and sequence homology, HSPs can be divided into five families: Hsp100s, Hsp90s, Hsp70s, Hsp60s, and Hsp20s, among which, Hsp20s are considered the most abundant and complex members (Vierling, 1991). The molecular size of Hsp20s ranges from 12 to 42 kDa, and they are called small HSPs. Hsp20s function as ATP-independent molecular chaperones to prevent proteins from irreversible aggregation and play a fundamental role in plant-acquired thermotolerance processes (Waters, 2013). The ACD is flanked by a variable N-terminal domain and a short C-terminal extension, which performs two different functions (Waters and Vierling, 2020)
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