Editing of Rice Endosperm Plastidial Phosphorylase Gene OsPho1 Advances Its Function in Starch Synthesis

OsPho1 in Zhonghua 11 (ZH11) was edited using the clustered regularly interspaced short palindromic repeats- associated endonuclease 9 (CRISPR/Cas9) system. Two homozygous T1 mutants (cr-pho1-34 and cr-pho1-37) displayed a chalky endosperm with a white core, which significantly decreased 1000-grain weight. In addition, many rounded starch granules and abnormal amyloplasts were present in the central region of mutant endosperm cells with increased amylose and lipid contents, decreased total protein content, and altered physicochemical properties of starch. The OsPho1 protein is localized in chloroplasts, and quantitative real-time PCR (qRT-PCR) and β-glucuronidase (GUS) staining indicated that OsPho1 was highly expressed in seeds at 5 d after fertilization (DAF). OsPho1 mutations displayed close relationships with plastidial phosphoglucomutase and ADP- Glc pyrophosphorylase based on α-D-glucose-1P at different temperatures. Moreover, the expressions of starch metabolism- related genes were also altered in the mutant, and the over- expression of OsPho1 may cause grain chalkiness.