Ustilago maydissecretedT2ribonucleases, Nuc1 and Nuc2 scavenge extracellularRNA

Ustilago maydisgenome codes for many secreted ribonucleases. The contribution of two among these belonging to the T2 family (Nuc1 and Nuc2) in the pathogen virulence, has been assessed in this study. Thenuc1andnuc2deletion mutants showed not only reduced pathogenicity compared to the SG200 WT strain but also exhibited significant delay in the completion of the pathogenic lifecycle. Both the proteins were also tested for their nucleolytic activities towards RNA substrates from maize and yeast. This also yielded valuable insights into the ability of the ribonucleases to utilise extracellular RNA as a nutrient source. Our study therefore established a role of two T2 type secreted ribonucleases of a phytopathogen in the acquisition of nutrient for the first time. This study also provides evidence that maize apoplast contains RNA, which can be utilised as a substrate by both Nuc1 and Nuc2.