Naturally occurring substitution of an amino acid in a plant virus gene-silencing suppressor enhances viral adaptation to increasing thermal stress

Author summaryClimate change and extreme weather events pose an increased risk for crops to become infected with pathogens, which could severely affect global food security. However, the studies about the effects of climate change on plant virus diseases are still obscure. Yellow dwarf disease is one of the most important diseases of small grain cereals worldwide, which is caused by viruses belonging to the genera Luteovirus and Polerovirus. The gene encoding the P0 protein of poleroviruses has been reported to be the most rapidly evolving ORF of the Polerovirus genus. P0 functions as a viral suppressor of RNA silencing (VSR) and the strength of silencing suppression of P0 is highly variable among CYDV-RPV isolates. However, little is known about the molecular mechanism that determine P0 suppressor activity. Here, we identify a naturally occurring, single-amino-acid substitution in the CYDV-RPV P0 protein that enhances its protein stability to increasing thermal stress. This is the first study to identify a naturally occurring amino acid substitution in a plant virus-encoded protein that determines its adaption to increasing thermal stress. As climate change and extreme weather events occur frequently, we expect that our research can supply insight into how a plant RNA virus evolves to adapt climate change. Cereal yellow dwarf virus (CYDV-RPV) encodes a P0 protein that functions as a viral suppressor of RNA silencing (VSR). The strength of silencing suppression is highly variable among CYDV-RPV isolates. In this study, comparison of the P0 sequences of CYDV-RPV isolates and mutational analysis identified a single C-terminal amino acid that influenced P0 RNA-silencing suppressor activity. A serine at position 247 was associated with strong suppressor activity, whereas a proline at position 247 was associated with weak suppressor activity. Amino acid changes at position 247 did not affect the interaction of P0 with SKP1 proteins from Hordeum vulgare (barley) or Nicotiana benthamiana. Subsequent studies found P0 proteins containing a P247 residue were less stable than the P0 proteins containing an S247 residue. Higher temperatures contributed to the lower stability and in planta and the P247 P0 proteins were subject to degradation via the autophagy-mediated pathway. A P247S amino acid residue substitution in P0 increased CYDV-RPV replication after expression in agroinfiltrated plant leaves and increased viral pathogenicity of P0 generated from the heterologous Potato virus X expression vector system. Moreover, an S247 CYDV-RPV could outcompete the P247 CYDV-RPV in a mixed infection in natural host at higher temperature. These traits contributed to increased transmission by aphid vectors and could play a significant role in virus competition in warming climates. Our findings underscore the capacity of a plant RNA virus to adapt to climate warming through minor genetic changes in gene-silencing suppressor, resulting in the potential for disease persistence and prevalence.