Geminiviral βC1 orchestrates organellar genomic instability to augment viral infection by hijacking host RecA

Chloroplast is the site for transforming light energy to chemical energy. It also acts as a production unit for a variety of defense-related molecules. These defense moieties are necessary to mount a successful counter defence against pathogens including viruses. Geminiviruses disrupt chloroplast homeostasis as a basic strategy for their successful infection inducing vein-clearing, mosaics and chlorosis in infected plants. Here we show that a geminiviral pathogenicity determinant protein βC1 directly interferes with plastid homeostasis. βC1 was capable of inducing organelle-specific nuclease to degrade plastid genome as well as diverted functions of RecA1 protein, a major player in plastid genome maintenance. βC1 interacted with RecA1 in plants and its homolog in bacteria to reduce the ability of host cells to maintain genomic integrity under stresses. Further, reduction in the coding capacity of plastids severely affected retrograde signalling necessary for viral perception and activation of defense. Induction of chloroplast-specific nuclease by βC1 is similar to phosphate starvation-response in which nucleotides are recycled to augment synthesis of new, potentially viral, DNA. These results indicate the presence of a novel strategy in which a viral protein alters host defence by targeting regulators of chloroplast DNA. We predict that the mechanism identified here might have similarities in other plant-pathogen interactions.

Phyllagathis chongzuoensis (Melastomataceae), a new species from Guangxi, China

Phyllagathis chongzuoensis, a new species from Guangxi Province, China, is described here. It is similar to P. erecta in having stiffly papery leaf blades with abaxially furfuraceous indumentum, similar leaf vernation, umbellate paniculate inflorescences and cup-shaped capsules, but differs in stoloniferous stem with indistinct internodes, shorter petioles, and obovate to suborbicular leaf blades with irregularly denticulate margin. Phylogenetic analyses based on nrITS and plastid genome confirmed that it is close to P. erecta.