Deciphering the differential physiological and molecular requirements for conidial anastomosis tube fusion and germ tube formation in Colletotrichum gloeosporioides

Abstract

AbstractThe conidia of a hemibiotrophic fungus Colletotrichum gloeosporioides can conventionally form germ tube (GT) and develop in to a fungal colony, while under certain conditions, they tend to get connected with each other through conidial anastomosis tube (CAT) so as to share the nutrients. CAT fusion is believed to be responsible for generation of genetic variations in few asexual fungi, which appears problematic for effective fungal disease management. The physiological and molecular mechanism underlying the GT versus CAT formation remained unexplored. In the present study, we have deciphered the decision switch responsible for GT formation versus CAT fusion in C. gloeosporioides. GT formation occurred at high frequency in the presence of nutrients, while CAT fusion was found to be higher in absence of nutrients. Younger conidia were found to form GT efficiently, whilst older conidia preferentially formed CAT. Whole transcriptome analysis of GT and CAT fusion revealed differential molecular requirements for these two processes. We identified 11050 and 9786 differentially expressed genes (DEGs) in GT and CAT, respectively. A total 1567 effector candidates were identified, of them 103 and 101 were uniquely secreted during GT and CAT formation respectively. Genes coding for cell wall degrading enzymes, germination, hyphal growth, host-fungus interaction and virulence were up-regulated during GT formation. Whilst, genes involved in stress response, cell wall remodelling, membrane transport, cytoskeleton, cell cycle, and cell rescue were highly up-regulated during CAT fusion. To conclude, the GT and CAT fusion were found to be mutually exclusive processes, requiring differential physiological conditions and sets of DEGs in C. gloeosporioides. This will help to understand the basic CAT biology in the genus Colletotrichum.