Phytochrome Signaling in Rice Immunity: Mechanisms, Trade-Offs, and Translational Opportunities

Light is a major environmental signal that regulates plant growth, development, and stress responses. Phytochromes are red/far-red light photoreceptors that integrate environmental light cues with transcriptional, hormonal, and physiological programs related to immunity and agronomic performance. Although most knowledge of phytochrome function comes from work on Arabidopsis thaliana and rice ( Oryza sativa )-specific evidence remains limited, recent studies have expanded our understanding of rice phytochrome functions beyond photomorphogenesis. For example, phytochrome B (OsphyB) contributes to blast resistance and affects yield-related traits, while PHYTOCHROME-INTERACTING FACTOR-LIKE proteins (OsPILs) connect light perception with defense, sugar allocation, tillering, and grain development. In this review, we summarize the rice phytochrome system and evaluate evidence linking phytochrome signaling to phytohormone-associated defense, reactive oxygen species signaling, calcium signaling, circadian regulation, and plant responses to light quality and temperature. We highlight recent mechanistic advances involving OsphyB-mediated tiller development and OsPIL15-dependent links among light signaling, immunity, and yield-related traits. These advances provide a framework for understanding how light signaling coordinates disease resistance with developmental and yield-related traits. We also discuss prospects for phytochrome-based breeding and genome editing, as well as questions that must be resolved before these strategies can be deployed in the field. Collectively, the available evidence positions phytochrome signaling as an emerging framework for understanding the coordination of immunity, development, and environmental acclimation in rice.