Genetic and Genomic Analysis Identifies bcltf1 as the Transcription Factor Coding Gene Mutated in Field Isolate Bc116, Deficient in Light Responses, Differentiation and Pathogenicity in Botrytis cinerea

Natural populations provide valuable information and resources for addressing the genetic characterization of biological systems. <i>Botrytis cinerea</i> is a necrotrophic fungus that exhibits complex responses to light. Physiological analysis of <i>B. cinerea</i> populations from vineyards in Castilla y León (Spain) allowed for the identification of isolate Bc116. This field isolate shows a reduced pathogenicity that is conditioned by the light regime. Light also delays germination and accentuates the negative effect it exerts on the vegetative growth of <i>B. cinerea</i>. Bc116 also displays a marked hyperconidiation phenotype and a characteristic sclerotia production pattern. Genetic analysis demonstrates that the alternative phenotypes regarding pathogenicity, conidiation, and pattern of sclerotia production co-segregate in the progeny of crosses between isolate Bc116 and a wild-type field isolate, Bc448, showing that they are under the control of a single <i>locus</i>. By applying a strategy based on bulked segregant analysis, the mutation in Bc116 has been mapped to a 200 kb region on Chr14 and the analysis of this region identifies a 2 kb deletion affecting the <i>bcltf1</i> gene, encoding the <i>B. cinerea</i> Light Responsive Transcription Factor 1 described in the reference isolate B05.10. Transformation of Bc116 with the B05.10 <i>bcltf1</i> allele restored the wild-type phenotypes, providing functional evidence that the natural mutant Bc116 is altered in gene <i>bcltf1</i>. This study offers additional information, derived from the analysis of the genetic background of a natural mutant, on the physiological processes regulated by BcLTF1 and supports the key role of this TF in the pathogenicity and photobiology of <i>B. cinerea</i>.