The PDI (Protein Disulfide Isomerase) gene family in wheat.

Abstract

The PDI (Protein Disulfide Isomerase) gene family includes several members whose products are responsible for diversified metabolic functions. PDI and PDI-like proteins differ for number and position of thioredoxin-like (TRX-like) active (a type) and inactive (b type) domains, for presence/absence of other domains and of the KDEL signal of retention in the endoplasmic reticulum (ER). The phylogenetic analysis of typical PDI and PDI-like protein sequences resolved them into 10 groups (1), 5 of them (I-V) had 2 TRX-like active domains, whereas the remaining ones owned only a single TRX-like active domain (VI-VIII, QSOX and APRL). In particular, QRX and APRL were not included in this study due to their putative non-isomerase enzymatic activities encoded by an additional domain. The aim of the present research was the study of the complexity and diversity of the PDI gene family in wheat, with particular focus on the genes encoding PDIlike proteins structurally similar to TaPDIL1-1 (group I), the first identified and best characterized member of the PDI family, also named typical PDI. The most important function of typical PDI is the formation and isomerization of disulfide bonds during protein folding, which are accomplished by its two active TRX-like sites sharing the characteristic tetrapeptide –CGHC-. Several studies of molecular characterization, expression analysis and cell localisation in rice and maize have suggested the involvement of typical PDI in the assembly and deposition of storage proteins in these species (2, 3, 4). The characterization and chromosome location of the three homoeologous gene sequences encoding typical PDI and of their promoter sequences have been reported previously (5).