Targeting of cucumber necrosis virus coat protein to the chloroplast stroma attenuates host defense response

Cucumber necrosis virus (CNV) is a (+)ssRNA virus that elicits spreading local and systemic necrosis in Nicotiana benthamiana. We previously showed that the CNV coat protein (CP) arm functions as a chloroplast transit peptide that targets a CP fragment containing the S and P domains to chlomplasts during infection. Here we show that several CP arm mutants that inefficiently target chlomplasts, along with a mutant that lacks the S and P domains, show an early onset of more localized necrosis along with protracted induction of pathogenesis related protein (PR1a). Agroinfiltrated CNV CP is shown to interfere with CNV p33 and Tomato bushy stunt virus p19 induced necrosis. Additionally, we provide evidence that a CP mutant that does not detectably enter the chloroplast stroma induces relatively higher levels of several plant defense-related genes compared to WT CNV. Together, our data suggest that targeting of CNV CP to the chloroplast stroma interferes with chloroplast-mediated plant defense.

Automated summary

Cucumber necrosis virus CP targets chloroplasts during infection, interfering with chloroplast-mediated plant defense. Mutants and truncations of the CP result in more severe necrosis and induction of specific genes.