Differential Expression of Cell Wall Remodeling Genes Is Part of the Dynamic Phase-Specific Transcriptional Program of Conidial Germination of Trichoderma asperelloides

Abstract

The nature of saprophytic and mycoparasitic hyphal growth of Trichoderma spp. has been studied extensively, yet its initiation via conidial germination in this genus is less well understood. Using near-synchronous germinating cultures of Trichoderma asperelloides, we followed the morphological progression from dormant conidia to initial polar growth to germling formation and to evidence for first branching. We found that the stage-specific transcriptional profile of T. asperelloides is one of the most dynamic described to date: transcript abundance of over 5000 genes—comprising approximately half of the annotated genome—was unremittingly reduced in the transition from dormancy to polar growth. Conversely, after the onset of germination, the transcript abundance of approximately a quarter of the genome was unremittingly elevated during the transition from elongation to initial branching. These changes are a testimony to the substantial developmental events that accompany germination. Bayesian network analysis identified several chitinase- and glucanase-encoding genes as active transcriptional hubs during germination. Furthermore, the expression of specific members of the chitin synthase and glucan elongase families was significantly increased during germination in the presence of Rhizoctonia solani—a known host of the mycoparasite—indicating that host recognition can occur during the early stages of mycoparasite development.

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“…The authors’ analyses revealed new and important aspects of early fungal ingress in F. graminearum that can form the basis for improvement of antifungal strategies, including a comparative gene expression finding that toxisomes are not fully functional until after penetration of the host cells. Based on a study using near-synchronous germinating cultures of T. asperelloides (a strain used in biocontrol that was formerly identified as T. asperellum ), it has been reported that the transcript abundance of half of the annotated genome is reduced during early conidial germination ( Grotikov et al., 2022b ). In this study, it was also discovered that the expression of the chitin synthase and glucan elongase families is significantly increased during germination in the presence of a basidiomycete host, Rhizoctonia solani (Ceratobasidiaceae, Cantharellales), indicating that host recognition can occur during the early stages of mycoparasite development ( Grotikov et al., 2022b ).…”

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“…Chitinases are also present in morphogenesis, acting in cell growth and expansion of these fungi, as reported for the fungus Trichoderma asperelloides; its 17 chitinase genes are expressed during germination of the microorganism's conidia (GORTIKOV et al, 2022).…”

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“…Its hydrophobic wall allows it to be transported by the wind while remaining dormant, until it finds an environment with enough nutrients to activate its metabolism [42]. From this moment on, the conidium starts so-called isotropic growth [43]. After approximately 6-8 h, it develops into a germ tube [44].…”