Characterisation of genes encoding cyclophilins and protein disulphide isomerases in cereals

The storage protein quality of wheat is important for nutritional and food technological purposes. ER-localised cyclophilins (Cyps) and protein disulphide isomerases (PDIs) are expected to play crucial roles in the deposition of storage protein in cereals. Large Cyp and PDI-like (PDIL) gene families have been identified in Arabidopsis and their putative proteins show numerous potential functions. However, limited information exists about the Cyp and PDI gene families in cereals. This study aimed to identify and characterise the Cyp and PDI gene families in wheat and rice using bioinformatics approaches and conduct comparative molecular and phylogenetic analysis with their orthologues in Arabidopsis. Another main aim was to experimentally identify and investigate the Cyp and PDI genes that potentially encode endoplasmic reticulum-localised proteins. Cyp family members (33 in rice, 22 in wheat) and PDIL family members (28 in rice, 27 in wheat) were identified using bioinformatics tools. In addition to the expected CypB genes, ove, two more putative ER-localised Cyps were identified in wheat and these may have potential roles in storage protein regulation. CypB genes were also isolated experimentally from common wheat and its progenitors. The genomic and cDNA sequences were cloned and the gene structure exhibited seven exons and six introns. The putative ER-localised CypB protein translated from exon contig from the B genome gene contains all PPIase signature sites, an N-terminal ER signal peptide, and an atypical C-terminal ER localisation signal. The putative promoter sequences were cloned and exhibit several potential tissue specific regulatory elements. The common wheat CypB genes are localised to chromosomes 7AL, 7BL and 7DL. In addition to the three reported ER-localised PDI homologues, five more putative ERlocalised PDIs were identified in wheat. Expression of three reported PDI homologues in developing seeds as well as stems and leaves, supports the hypothesis that PDI plays a role in vegetative tissues as well as in the developing endosperm. Collectively, the work has identified new Cyps and PDIs with potential roles in storage protein folding function, response to ER and other stresses, grain quality and other important traits.