Optimizing the Agrobacterium tumefaciens-mediated transformation conditions in Colletotrichum lindemuthianum: a step forward to unravel the functions of pathogenicity arsenals.

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Colletotrichum lindemuthianum is a hemibiotrophic fungal pathogen that causes bean anthracnose and it is rated among the top 10 important diseases infecting beans. Currently our knowledge on molecular mechanisms underlying C. lindemuthianum pathogenesis is limited. About five pathogenicity genes have been identified in C. lindemuthianum using Restricted Enzyme Mediated Integration and the transformation using Agroinfection has not been optimized. In this study, a series of experiments were conducted to optimize the key parameters affecting the Agrobacterium tumefaciens-mediated transformation for C. lindemuthianum. The transformation efficiency increased with increase in spore concentration and co-cultivation time. However, the optimum conditions that yielded significant number of transformants were 106 ml-1 spore concentration, co-cultivation time of 72 h, incubation at 25°C and using a cellulose membrane filter for the co-cultivation. The optimized protocol resulted in establishment of large mutant library (2400). A few mutants were melanin deficient and a few were unable to produce conidia. To determine the altered pathogenicity, two new approaches such as detached leaf and twig techniques proved reliable and require fewer resources to screen the large mutant libraries in a short time. Among the 1200 transformants tested for virulence, 90% transformants were pathogenically similar to wild type (race 2047), 96 and 24 were reduced and impaired, respectively. The altered avirulent transformants can prove vital for understanding the missing link between growth and developmental stages of pathogen with virulence. This platform will help to develop strategies to determine the potential pathogenicity genes and to decipher molecular mechanisms of host-pathogen interactions in more detail.