The OsABCI7 Transporter Interacts with OsHCF222 to Stabilize the Thylakoid Membrane in Rice

Abstract

The thylakoid membrane is a highly complex membrane system in plants and plays crucial roles in the biogenesis of the photosynthetic apparatus and plant development. However, the genetic factors involved in chloroplast development and its relationship with intracellular metabolites are largely unknown. Here, a rice (<i>Oryza sativa</i>) <i>chlorotic and necrotic leaf1</i> (<i>cnl1</i>) mutant was identified and map-based cloning revealed that a single base substitution followed by a 6-bp deletion in the <i>ATP-binding cassette transporter I family member7</i> (<i>OsABCI7</i>) resulted in chlorotic and necrotic leaves with thylakoid membrane degradation, chlorophyll breakdown, photosynthesis impairment, and cell death in <i>cnl1</i> Furthermore, the expression of <i>OsABCI7</i> was inducible under lower temperatures, which severely affected <i>cnl1</i> chloroplast development, and etiolated <i>cnl1</i> seedlings were unable to recover to a normal green state under light conditions. Functional complementation and overexpression showed that <i>OsABCI7</i> could rescue the <i>cnl1</i> chlorotic and necrotic phenotype. OsABCI7 interacted with HIGH CHLOROPHYLL FLUORESCENCE222 (OsHCF222) to regulate cellular reactive oxygen species (ROS) homeostasis for thylakoid membrane stability. OsABCI7 localized to thylakoid membranes, while OsHCF222 targeted to endoplasmic reticulum and chloroplasts. Exogenous application of ascorbic acid eased the yellowish leaf phenotype by increasing chlorophyll content and alleviating ROS stress in <i>cnl1</i> Unlike <i>cnl1</i>, the CRISPR/Cas9-mediated <i>OsHCF222</i> knockout lines showed chlorotic leaves but were seedling lethal. Our results provide insight into the functions of ABC transporters in rice, especially within the relationship between ROS homeostasis and stability of thylakoid membranes.