Role of OsABA8ox2 in the regulation of seedling establishment and grain filling in rice

Seedling establishment and grain filling are two important processes in rice life cycle. The former provides the solid basis for rapid canopy construction, while the latter is the key process for yield formation. Many earlier studies have proved that abscisic acid (ABA) plays key roles in these two biological processes and the physiology involving ABA has been well illustrated. However, the molecular mechanism of how ABA catabolism regulates seedling establishment and grain filling is still poorly understood. It is known that ABA content in plants is controlled by an antagonism between ABA biosynthesis and ABA catabolism. Many studies on ABA functions have focused on the ABA biosynthesis and ABA signalling pathway, while little is known about the biological significance and the role of ABA catabolism, especially during the early seedling establishment and the later grain filling process.

We have found an ABA catabolism gene, OsABA8ox2, that displays multiple effects in regulating seedling establishment and grain filling in rice. Overexpression of OsABA8ox2 (OsABA8ox2OE) results in an inhibition of seedling establishment and grain filling, while knockout of OsABA8ox2 (OsABA8ox2KO) by CRISPR/Cas9 can significantly promote grain filling of inferior (the later flowering) spikelets without obvious effect on seedling establishment. Application of ABA and H2O2 can significantly rescue the root growth of OsABA8ox2OE plant, while OsABA8ox2KO plant is much more sensitive to ABA treatment. Interestingly, increase or suppress expressions of other ABA biosynthesis and catabolism genes, such as OsNCED3 and OsABA8ox3, did not lead to similar phenotypes, suggesting that OsABA8ox2 gene plays a unique function in these two biological processes.

Based on our preliminary results, we plan to utilize plant molecular biology approaches and reverse genetic technology to investigate the molecular mechanism that regulates the ABA level through OsABA8ox2 and other possible related genes, as well as the molecular mechanism of controlling seedling establishment and grain filling by OsABA8ox2 and ABA in rice. We also hope to create some new germplasms by gene editing on elite rice cultivars with better grain filling efficiency. The results of this study will provide new insight for the phytohormone-controlled plant growth and development and genetic resources for rice breeding and cultivation.