Identification and analysis of genes encoding a novel ER-localised Cyclophilin B in wheat potentially involved in storage protein folding

The storage protein deposition processes in cereal endosperm follow a strict script involving protein folding and refolding, assortment and protein body deposition by two distinct pathways. The endoplasmic reticulum-localised enzymes called peptidyl prolyl cis-trans isomerases (PPIases) are expected to play crucial 'foldase' and chaperone roles in the deposition of wheat prolamins due to their proline-rich nature. The storage protein quality of wheat is important for nutritional and food technological purposes; however, little information exists on genetic control of protein sorting and deposition processes. In this study, CypB genes encoding an ER-localised cyclophilin (a PPIase) have been characterised from common wheat (Triticum aestivum L. AABBDD) and its progenitors for the first time. The full-length genes contain seven exons and six introns, the exons being significantly more conserved. The putative CypB protein contains all PPIase signature sites including the putative active site and cyclosporin-binding residues, but an atypical ER localisation signal. Using the sequence variations, the common wheat genes were localized to chromosomes 7AL, 7BL and 7DL. The promoters of wheat genes were identified by inverse-PCR and show a number of potential tissue specific regulatory elements. The wheat genes are similar in structure to rice CypB and the putative proteins are 83% identical. Further, certain QTLs related to protein quality occur at the rice and wheat CypB loci. The results support this enzyme being a strong candidate for regulating storage protein quality in wheat.