Identification and characterization of 20S proteasome genes and their relevance to heat/drought tolerance in bread wheat

The genes encoding α- and β-type subunits of 20S proteasome core protease are integral components of 26S proteasome complex in the ubiquitin-proteasome system (UPS). The 20S proteasome represents a catalytic particle that cleaves cytotoxic, denatured, damaged and unwanted proteins in an ATP/ubiquitin-dependent non-lysosomal pathway and is known to impart thermotolerance in model plants. In the present study, we identified 67 genes (including 34 TaPA + 33 TaPB genes) encoding α- and β-subunits of 20S proteasome in bread wheat (Triticum aestivum L.). These genes were distributed on all the 21 wheat chromosomes, majority of them being in triplicate homoeologues. These wheat genes were orthologous to corresponding rice and Arabidopsis genes. Phylogenetic analysis placed these genes in seven clusters, each with one of the seven α (α1-7) and one of the seven β (β1-7) subunits. Expression analysis suggested that 10 of the 67 genes were involved in heat stress response, whereas four genes were involved in drought tolerance at the seedling stage. Nine (9) genes were expressed under both heat and drought suggesting their involvement in response to multiple abiotic stresses. Hopefully, future research on TaPA/TaPB genes, will help in the development of climate resilient wheat cultivars.