A polygalacturonase gene OsPG1 modulates water homeostasis in rice

A dynamic plant architecture is the basis of plant adaptation to changing environments. Although many genes regulating leaf rolling have been identified, genes directly associated with water homeostasis are largely unknown. Here, we isolated a rice mutant, dynamic leaf rolling 1 (dlr1), characterized by ‘leaf unfolding in the morning-leaf rolling at noon-leaf unfolding in the evening’ during a sunny day. Water content was decreased in rolled leaves and water sprayed on leaves caused reopening, indicating that in vivo water deficiency induced the leaf rolling. Map-based cloning and expression tests demonstrated that an A1400G single base mutation in Oryza sativa Polygalacturonase 1 (OsPG1)/PHOTO-SENSITIVE LEAF ROLLING 1 (PSL1) was responsible for the dynamic leaf rolling phenotype in the dlr1 mutant. OsPG1 encodes a polygalacturonase, one of the main enzymes that degrade demethylesterified homogalacturonans in plant cell walls. OsPG1 was constitutively expressed in various tissues and was enriched in stomata. Mutants of the OsPG1 gene exhibited defects in stomatal closure and decreased stomatal density, leading to reduced transpiration and excessive water loss under specific conditions, but had normal root development. Further analysis revealed that mutation of OsPG1 led to reduced pectinase activity in the leaves and increased demethylesterified homogalacturonans in guard cells. Our findings reveal a mechanism by which OsPG1 modulates water homeostasis to control dynamic leaf rolling, providing insights for plants to adapt to environmental variation.