Heat Shock Protein 20 Gene Superfamilies in Red Algae: Evolutionary and Functional Diversities

Abstract

Heat shock protein 20 (<i>Hsp20</i>) genes play important roles in plant growth, development, and response to environmental stress. However, the <i>Hsp20</i> gene family has not yet been systematically investigated, and its function in red algae (Rhodophyta) remains poorly understood. Herein, we characterized <i>Hsp20</i> gene families in red algae by studying gene structure, conserved motifs, phylogenetic relationships, chromosome location, gene duplication, <i>cis-</i>regulatory elements, and expression profiles. In this study, 97 <i>Hsp20</i> genes were identified using bioinformatic methods and classified into 13 subfamilies based on phylogenetic relationships. Phylogenetic analysis revealed that <i>Hsp20</i> genes might have a polyphyletic origin and a complex evolutionary pattern. Gene structure analysis revealed that most <i>Hsp20</i> genes possessed no introns, and all <i>Hsp20</i> genes contained a conserved α-crystalline domain in the C-terminal region. Conserved motif analysis revealed that <i>Hsp20</i> 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 <i>Hsp20</i> genes in <i>Pyropia yezoensis</i>, <i>Pyropia haitanensis</i>, and <i>Porphyra umbilicalis</i> were highly evolutionarily conserved. The <i>cis-</i>elements of phytohormone-, light-, stress-responsive, and development-related were identified in the red algal <i>Hsp20</i> gene promoter sequences. Finally, using <i>Py. yezoensis</i>, as a representative of red algae, the <i>Hsp20</i> gene expression profile was explored. Based on the RNA-seq data, <i>Py. yezoensis Hsp20</i> (<i>PyyHsp20)</i> genes were found to be involved in <i>Py. yezoensis</i> responses against abiotic and biotic stresses and exhibited diverse expression patterns. Moreover, <i>PyyHsp20</i> is involved in <i>Py. yezoensis</i> growth and development and revealed spatial and temporal expression patterns. These results provide comprehensive and valuable information on <i>Hsp20</i> gene families in red algae and lay a foundation for their functional characterization. In addition, our study provides new insights into the evolution of <i>Hsp20</i> gene families in red algae and will help understand the adaptability of red algae to diverse environments.