Genome-Wide Identification And Characterization Of Tomato E2 Ubiquitin–Conjugating Enzymes In Plant Immunity

Plants can be attacked by various pathogens throughout their life cycle and host immune system plays a critical role in warding off such attacks.  Studies in the past two decades have implicated a complex of mechanisms in the regulation of plant immunity, among which ubiquitination has emerged in recent years as an important player.  Increasing evidences indicate that E2 ubiquitin-conjugating enzymes play a key role in regulating mammalian immunity.  Nevertheless until now the roles of E2s in plant immunity are virtually unknown.  Based on our previous experiment we hypothesize that E2 enzymes are actively involved in plant immunity as well.  To test this, we have identified a near-complete set of genes encoding E2 ubiquitin-conjugating enzymes from tomato genome by an array of whole-genome analysis algorithms.  All the identified genes are supported by either ESTs and/or full-length cDNA.  Phylogenetic analysis indicates most tomato E2 genes find their homologs in Arabidopsis though proteins encoded by many of them share highest similarity to another tomato E2 protein, which suggests gene duplications in the evolution of tomato genome.  Gene expression profiling using data collected in online database reveals several Arabidopsis homologs of tomato E2 genes are significantly differentially expressed after pathogen challenge, implying their involvement in host immunity.  The tomato closest counterparts of these genes have been chosen for further investigations. Biochemical analysis indicated that the majority of tested tomato E2 enzymes are active E2s.  Further functional characterization of these genes is undergoing.