Pathogenically altered Colletotrichum lindemuthianum transformants help in understanding the biochemical defense and colonization dynamics in Phaseolus vulgaris

Abstract

Colletotrichum lindemuthianum poses a serious threat to common bean production and impacts food security. It is essential to comprehend the intricate nature of the pathogen infection process and the underlying biochemical systems regulating plant defence to create tactics that effectively increase plant resistance. This study leveraged a stable C. lindemuthianum transformant library to examine these intrinsic mechanisms in a susceptible Phaseolus vulgaris cultivar, Jawala. Among the 57 mitotically stable transformants employed to screen for altered virulence, 51 were pathogenically similar to wild type and the remaining six transformants were either reduced or impaired. Nine transformants (three pathogenically similar and all impaired and reduced mutants) were selected for subsequent studies. These mutants exhibited an array of morpho-cultural variations. The biochemical studies of these mutants revealed free radicals as double-edged swords, exerting a pivotal influence on the infection process. The free radical (H2O2) elevated at an early stage (24 hpi) in the cases of reduced (CT-51) and impaired (CT-225) mutants. However, at the later stage (72 hpi), H2O2 was promoted in the case of R-2047 and equal to wild type (CT-101) transformant. Contrary, superoxide (O2−) increased considerably at 48 hpi in the incompatible interaction of reduced (CT-51) and impaired (CT-225) mutants. The microscopic images revealed how easily the wild type (CT-101) could germinate, penetrate, and infect the leaves. The pathogenically reduced transformant (CT-51), however, had delayed germination as well as a decreased growth rate and spore production. Additionally, the pathogenicity of the impaired transformant (CT-225) was completely lost, and its conidia failed to properly germinate. This is the first account of C. lindemuthianum in planta colonization with a GFP tag. This study increased our understanding of the mechanics of the reactions triggered by C. lindemuthianum and may be used to develop novel strategies for the effective control of bean anthracnose. Additionally, identifying the genes disrupted by the insertion of Agrobacterium T-DNA will help in identifying the genes necessary for bean plant colonization.