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

Nikita Mehta,Abhishek Baghela

doi:10.1186/s43008-021-00058-y

Nikita Mehta, Abhishek Baghela

Open Access

https://doi.org/10.1186/s43008-021-00058-y

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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 CAT fusion between two important plant fungal pathogens Colletotrichum gloeosporioides and C. siamense. In an invitro assay, under no selection pressure, the inter-specific CAT fusion was preferred with higher frequency (25% ± 5%) than intra-specific CAT fusion (11% ± 3.6%). 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 under physiological stresses. This CAT fusion involved a quorum sensing phenomenon, wherein the CAT induction was dependent on conidial density and the putative quorum sensing molecule was extractable in chloroform. Movement of nuclei, mitochondria, and lipid droplets were observed during the CAT fusion. Post CAT fusion, the resulting conidia gave rise to putative heterokaryotic progenies with variable colony characteristics as compared to their parental strains. Few heterokaryons showed variable AFLP banding pattern compared to their parental strains, thereby suggesting a possible genetic exchange between the two species through CAT fusion. The heterokaryotic progenies exhibited varied fitness under different stress conditions. Our study illustrated a possible role of inter-specific CAT fusion in generation of genetic and phenotypic diversity in these fungal pathogens.

Highlights

Colletotrichum is a widespread genus voted as the eighth most important group of plant pathogenic fungi in the world (Dean et al 2012)
When different aged conidia of C. gloeosporioides and C. siamense were analyzed individually for Conidial anastomosis tube (CAT) fusion, it was observed that the CAT fusion occurred in very low frequency in 6 days old conidia and thereafter percentage of CAT fusion increased with the increasing age of conidia
It was observed that when 17 days old conidia of C. gloeosporioides and C. siamense were incubated in distilled water for 24, 48, 72 and 96 h separately, the maximum CAT fusion frequency was observed at 72 h post-incubation (ANOVA + Tukey’s post-hoc test, n = 3, p < 0.05) (Fig. 2E)

Summary

Introduction

Colletotrichum is a widespread genus voted as the eighth most important group of plant pathogenic fungi in the world (Dean et al 2012). C. gloeosporioides and C. siamense cause infection in a wide range of host plants (Cai et al 2009; Freeman et al 1996; Hyde et al 2009; Jayawardena 2018; Sharma et al 2013). We have previously reported a high level of genetic diversity in C. gloeosporioides isolates in India (Mehta et al 2017). The possible mechanism that gives rise to such high genetic diversity may lie in meiotic recombination during sexual reproduction, it has been suggested that sexual reproduction in C. gloeosporioides in nature would be rare, if not absent (da Silva et al 2020; Weir et al 2012). Sexual stage for C. siamense has not been demonstrated to date (Prihastuti et al 2009)

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