Quorum sensing-mediated inter-specific conidial anastomosis tube fusion between Colletotrichum gloeosporioides and Colletotrichum siamense.

Abstract Many plant pathogenic filamentous fungi undergo fusion of conidia through conidial anastomosis tubes (CATs), which is believed to facilitate horizontal gene transfer between species. We discovered a remarkable inter-specific conidial anastomosis tube (CAT) fusion between two important plant fungal pathogens Colletotrichum gloeosporioides and Colletotrichum siamense. In an In vitro assay, under no selection pressure, the inter-specific CAT fusion was preferred with higher frequency (25%) than intra-specific CAT fusion (11%). Different stages of CAT fusion viz. CAT induction, homing, and fusion were observed during this inter-specific CAT fusion. The CAT fusion was found to be higher in absence of nutrients and in the presence of physiological stresses. This CAT fusion involved a quorum sensing phenomenon, wherein the CAT induction was dependent on conidial density and the secreted putative quorum sensing molecules were found to be lipid based in nature. Movement of nuclei, mitochondria, lysosomes and lipid droplets were observed during the CAT fusion. Post CAT fusion, the resulting conidia gave rise to putative recombinants with variable colony characteristics as compared to their parental strains. Few recombinants showed variable AFLP banding pattern compared to their parental strains, thereby suggesting a possible genetic exchange between the two species through CAT fusion. The recombinants exhibited variable fitness under different stress conditions. Our study signifies possible role of inter-specific CAT fusion in generation of genetic and phenotypic diversity in these fungal pathogens.