Abstract
VelA (or VeA) is a key global regulator in fungal secondary metabolism and development which we previously showed is required during the symbiotic interaction of Epichloë festucae with perennial ryegrass. In this study, comparative transcriptomic analyses of ∆velA mutant compared to wild-type E. festucae, under three different conditions (in culture, infected seedlings, and infected mature plants), were performed to investigate the impact of VelA on E. festucae transcriptome. These comparative transcriptomic studies showed that VelA regulates the expression of genes encoding proteins involved in membrane transport, fungal cell wall biosynthesis, host cell wall degradation, and secondary metabolism, along with a number of small secreted proteins and a large number of proteins with no predictable functions. In addition, these results were compared with previous transcriptomic experiments that studied the impact of LaeA, another key global regulator of secondary metabolism and development that we have shown is important for E. festucae–perennial ryegrass interaction. The results showed that although VelA and LaeA regulate a subset of E. festucae genes in a similar manner, they also regulated many other genes independently of each other suggesting specialised roles.
Highlights
Epichloë endophytes are symbiotic fungi that systematically colonize intercellular spaces of cool-season grasses of the subfamily Pooideae [1,2,3]
LaeA is a global fungal regulator and a predicted interaction partner of VelA [36] which we recently reported is required for E. festucae metabolism and development and for establishing and maintaining a successful symbiotic interaction with perennial ryegrass [12]
In order to investigate the regulatory effects of VelA on secondary metabolism in E. festucae, the differential expression of genes involved in known alkaloid gene clusters was examined across all comparisons
Summary
Epichloë endophytes are symbiotic fungi that systematically colonize intercellular spaces of cool-season grasses of the subfamily Pooideae [1,2,3]. The molecular mechanisms that regulate the mutualistic interaction between E. festucae and perennial ryegrass are still largely unknown, a number of studies have shown the importance of genes required for hyphal anastomosis (soft gene [10]), fungal biology and development (velA gene [11] and laeA gene [12]), localised production of reactive oxygen species (required to maintain hyphal polarity [13,14,15,16]), and iron homeostasis (sidN gene [17,18]). Studies of ∆velA differential expression compared with wild-type fungi in different conditions have mostly used microarrays These studies showed that VelA regulates genes involved in different fungal developmental and metabolism processes, coordinating with the functional analysis of the mutants. There are 182 DEGs common in the transcriptomes of three E. festucae mutants (∆proA, ∆noxA, and ∆sakA), which were proposed to form a core set of Epichloë genes that distinguished mutualistic from antagonistic symbiotic states [20]. The expression of other members of the velvet family did not change significantly in any of the ∆velA or ∆laeA mutants (Table S4)
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