Analysis of isolation and expression analysis of ItCYP79B2 during rust infection of dyer's woad (Isatis tinctoria) by Puccinia thlaspeos

Abstract

Dyer's woad (Isatis tinctoria) has been shown to have unusually high quantities of indole glucosinolates. It is known that production of glucosinolates and their hydrolysis products is part of a plant's defense response to pathogens and insects. In Arabidopsis thaliana, which, like dyer's woad, is in the family Brassicaceae, the gene sequences encoding CYP79B2 and CYP79B3 catalyze the conversion of tryptophan to indole-3-acetaldoxime during the biosynthesis of indole glucosinolates. In this study, a sequence encoding CYP79B2 was isolated from dyer's woad. ItCYP79B2 from I. tinctoria shows 97% sequence identity with CYP79B2 and 89% sequence identity with CYP79B3 from A. thaliana. Thus, it can be inferred that the I. tinctoria sequence, like that of A. thaliana, is involved in the biosynthesis of indole glucosinolates. The kinetics and amplitude of ItCYP79B2 expression during the first 72 h after infection by the pathogenic rust fungus Puccinia thlaspeos were also studied. There was a significant down-regulation of ItCYP79B2 during the first 8 h after infection of the host that coincides with fungal penetration. This was followed by induction of ItCYP79B2, coinciding with the formation of haustoria. However, after haustoria formation, ItCYP9B2 was again suppressed during the time period coinciding with successful asymptomatic systemic colonization of the host. The results of this study indicates that suppression of a gene involved in indole glucosinolate production during the penetration and post-haustorial phases of infection plays a role in pathogen establishment. They also imply that the pathogen possesses mechanisms for circumventing the elevated expression of this gene during the haustorial phase