Pleiotropic effects of resistance-breaking mutations on particle stability provide insight on life history evolution in a plant RNA virus.

In gene-for-gene host-virus interactions, virus evolution to infect and multiply in previously resistant host genotypes, i.e., resistance-breaking, is a case of host range expansion, predicted to be associated with fitness penalties. Negative effects of resistance-breaking mutations on within-host virus multiplication have been documented for several plant viruses. However, understanding virus evolution requires analyses of potential trade-offs between different fitness components. Here we analyze if coat protein (CP) mutations in Pepper mild mottle virus breaking L -gene resistance in pepper affect particle stability and, thus, survival in the environment. For this purpose, CP mutations determining the overcoming of L3 and L4 resistance alleles were introduced in biologically active cDNA clones. The kinetics of the in vitro disassembly of parental and mutants' particles was compared under different conditions. Resistance-breaking mutations variously affected particle stability. Structural analyses identified the number and type of axial and side interactions of adjacent CP subunits in virions, which explained differences in particle stability and contribute to understand tobamovirus disassembly. Resistance-breaking mutations also affected virus multiplication and virulence in the susceptible host, as well as infectivity. The sense and magnitude of the effects of resistance-breaking mutations on particle stability, multiplication, virulence or infectivity depended on the specific mutation, rather than on the ability to overcome the different resistance alleles, and effects on different traits were not correlated. Thus, results do not provide evidence of links or trade-offs between particle stability, i.e., survival, and other components of virus fitness, or virulence. IMPORTANCE The effect of survival on virus evolution remains underexplored, despite that life history trade-offs may constrain virus evolution. We approach this topic by analyzing if breaking of L -gene resistance in pepper by Pepper mild mottle virus , determined by coat protein (CP) mutations, is associated with reduced particle stability and survival. Resistance-breaking mutations affected particle stability by altering the interactions between CP subunits. However, the sense and magnitude of these effects were unrelated to the capacity to overcome different resistance alleles. Thus, resistance-breaking was not traded with survival. Resistance-breaking mutations also affected virus fitness within the infected host, virulence and infectivity in a mutation-specific manner. Comparison of the effects of CP mutations on these various traits indicates that there are neither trade-offs nor positive links between survival and other life history traits. These results demonstrate that trade-offs between life-history traits may not be a general constraint in virus evolution.