A staging framework to study rice female gametophyte development

Female gametophyte (FG) development is essential for plant reproduction since it is necessary for pollen tube guidance, fertilization, and maternal control of seed development. FG development entails dynamic cellular and developmental changes including multiple cell divisions and cell differentiations with biologically distinct roles in fertilization, a critical process for grain yield in cereal crops. Rice (Oryza sativa) is a model monocotyledonous plant with invaluable relevance for food security as it is one of the most important staple food crops. Therefore, to study rice FG development, a robust and precise staging method is required to explore the molecular dynamics of this important organ. Here, we provide a pistil length-based staging framework for defining developmental stages in rice ovules. We systematically analyzed FG developmental progress using several reproductive morphological parameters. Six unique developmental stages that are morphologically distinguishable and encompass the entirety of FG development were identified. Using transcriptional expression of developmental marker genes that are temporally regulated during FG development we validated this staging method. Our method provides a systematic and accurate staging framework that could be used to explore temporally and developmentally dynamic molecular events during FG development, including transcriptional, epigenetic, and metabolic regulation.