CaLhcb1-like coordinates ROS dynamics and lignin accumulation to gate Ralstonia solanacearum resistance in pepper (Capsicum annuum)

Chloroplasts participate in plant-pathogen interactions by affecting reactive oxygen species (ROS) homeostasis, photosystem II (PSII) functionality, and spectral signature modulation. Focusing on light-harvesting complex II (LHCII) components, we characterized the role of CaLhcb1-like in pepper (Capsicum annuum) resistance to Ralstonia solanacearum. Comparative transcriptomic analysis of susceptible (HS03) and resistant (HR01) cultivars revealed genotype-specific expression patterns of CaLhcb1-like. Subcellular localization confirmed that CaLhcb1-like is chloroplast-targeted. Virus-induced gene silencing (VIGS) showed that CaLhcb1-like knockdown enhanced bacterial wilt resistance. This was accompanied by attenuated multispectral reflectance changes at 400-690 nm, altered PSII parameters (effective quantum yield, Fq'/Fm', and relative electron transport rate, ETR), biphasic ROS dynamics with an early burst before 2 hpi followed by a decline at 6 hpi, and upregulation of genes in plant-pathogen interaction and phenylpropanoid biosynthesis pathways. Biochemical assays further validated increased peroxidase activity and lignin accumulation in silenced lines. These findings demonstrate that CaLhcb1-like negatively regulates defense responses through ROS homeostasis and lignin accumulation, providing molecular links between multispectral variation and disease progression.