Genome-wide identification and characterization of the wall associated kinase gene family and expression analysis under high temperature stress in sorghum (Sorghum bicolor L. Moench)

Sorghum (Sorghum bicolor L. Moench) is the world's fifth most-produced cereal. The wall-associated kinases (WAKs) gene family plays a crucial regulatory role in growth and development in plants, in response to environmental stress and pathogens. This study aimed to characterize the members of the WAK gene family in sorghum using bioinformatics tools and to determine their functional roles under high temperature conditions. In sorghum, 31 WAK and 67 WAK-Like (WAKL) proteins were identified and named as SbWAK/SbWAKL. A total of 98 SbWAK/SbWAKL proteins were classified into six phylogenetic groups. The SbWAKs/SbWAKL genes were unevenly distributed across ten chromosomes, and 33 duplications were observed on nine. The number of amino acids and molecular weight of SbWAKs/SbWAKLs ranged from 496 to 1149 aa and 55.38 to 124.89 kDa, respectively. It was determined that SbWAKL5 and SbWAKL47 proteins were hydrophobic, while other proteins were hydrophilic. Forty-eight SbWAK/SbWAKL proteins were found to be unstable with an instability index value greater than 40. The synteny analyses revealed sixteen SbWAK/SbWAKL genes similar in foxtail millet, thirteen in maize, and seven in the rice genome. Ka/Ks values signify purifying selection and positive selection phenomenon on the genes. Additionally, protein-protein interactions of SbWAK/SbWAKL show that these proteins have many different functions. miRNA interaction analysis results showed that 107 miRNAs, including cell wall-associated miRNA families (miR156, miR164, miR397, miR528, miR5566, and miR6230), targeted 85 SbWAK/SbWAKL genes. To understand the functional roles of 13 SbWAK/SbWAKL genes under high temperature condition (42 °C for 4 h), their expression levels were analyzed by real-time quantitative polymerase reaction. A relatively high transcript increase rate was determined in SbWAK10, SbWAK22, SbWAK23, SbWAK31, SbWAKL12, and SbWAKL63 genes. In conclusion, cis-acting elements, protein-protein and miRNA interactions, and higher gene expression levels at high temperatures may indicate the existence of candidate SbWAKs/SbWAKLs genes with functions in abiotic and biotic stress response and their usage in future gene editing for breeding purposes.