Poster: Comparative Genomics

Abs # 926: Characterization of a plant-specific PDI class with novel protein properties

Presenter:	Houston, Norma L, nlhousto@unity.ncsu.edu
Authors	Houston, Norma L (A) (B)  Fan, Chuanzhu  (A)   Xiang, Qiu-Yun (Jenny)  (A)   Jung, Rudolf  (C)   Boston, Rebecca S (A) (B)
Affiliations:	(A): Department of Botany, North Carolina State University, Raleigh, NC (B): Functional Genomics Program, North Carolina State University, Raleigh, NC (C): Pioneer Hi-Bred International, Inc. Johnston, IA

One biological response to intracellular accumulation of non-native protein domains is the induction of molecular chaperones, including protein disulfide isomerases (PDIs). PDIs are encoded by a multigene family with characteristic domain structures containing active thioredoxin-like domains minimally composed of a CXXC tetrapeptide and a distinct fold pattern. One of the major chaperone functions of PDIs is to act as oxidoreductases that aid transition to a native protein conformation by shuffling illegitimate disulfide bonds. Generally, PDIs have a canonical ER retention signal and are induced by ER stress. Using BLAST analysis, we performed iterative searches to identify the PDI gene family in Arabidopsis, maize and rice. Phylogenetic analysis with both Bayesian and maximum likelihood methods suggested that PDIs from plants fall into seven major classes. At least four evolutionary duplications occurred in deep evolutionary time, probably before the diversification of major kingdoms of life forms and one duplication arose in early Eudicot evolution. In addition to an organization into these major classes, the phylogeny also implies that there were frequent duplications of PDI genes within different lineages of flowering plants. Two of the classes appear to be plant specific, one being the result of an ancient event and the second a result of a more recent duplication. Interestingly, the sequence of the more ancient plant-specific PDI clade is missing the canonical ER retention signal. An investigation of the maize member of this PDI clade, however, shows localization in luminal fractions of ER-enriched microsomes. In addition, this unusual PDI is induced during ER stress.