Generation of mRNA isoforms by alternative polyadenylation (APA) and their involvement in regulation of fungal cellular processes, including virulence, remains elusive. Here, we investigated genome-wide polyadenylation site (PAS) selection in the rice blast fungus to understand how APA regulates pathogenicity. More than half of Magnaporthe oryzae transcripts undergo APA and show novel motifs in their PAS region. Transcripts with shorter 3'UTRs are more stable and abundant in polysomal fractions, suggesting they are being translated more efficiently. Importantly, rice colonization increases the use of distal PASs of pathogenicity genes, especially those participating in signalling pathways like 14-3-3B, whose long 3'UTR is required for infection. Cleavage factor I (CFI) Rbp35 regulates expression and distal PAS selection of virulence and signalling-associated genes, tRNAs and transposable elements, pointing its potential to drive genomic rearrangements and pathogen evolution. We propose a noncanonical PAS selection mechanism for Rbp35 that recognizes UGUAH, unlike humans, without CFI25. Our results showed that APA controls turnover and translation of transcripts involved in fungal growth and environmental adaptation. Furthermore, these data provide useful information for enhancing genome annotations and for cross-species comparisons of PASs and PAS usage within the fungal kingdom and the tree of life.
Mercury (Hg) is one of the most hazardous pollutants released by humans and is of global environmental concern. Mercury causes oxidative stress and strong cellular damages in plants, which can be attenuated by the biosynthesis of thiol-rich peptides (biothiols), which include glutathione (GSH) and phytochelatins (PCs). We analysed Hg tolerance and speciation in five Arabidopsis thaliana genotypes, the wild-type Col-0, three knockdown γ-glutamylcysteine synthetase (γECS) mutants and a knockout PC synthase (PCS) mutant. Mercury-PC complexes were detected in roots by HPLC-ESI-TOFMS, with its abundance being limited in γECS mutants. Analysis of Hg-biothiol complexes in the xylem sap revealed that HgPC 2 occurs in wild-type Col-0 Arabidopsis, suggesting that Hg could be translocated associated with thiol-rich metabolites. Twenty genes involved in sulphur assimilation, GSH and PCs synthesis were differentially expressed in roots and shoots, implying a complex regulation, possibly involving post-translational mechanisms independent of GSH cellular levels. In summary, the present study describes the importance of biothiol metabolism and adequate GSH levels in Hg tolerance, and identifies for the first time Hg-PC complexes in the xylem sap. This finding supports that Hg-biothiol complexes could contribute to Hg mobilisation within plants.
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