Abstract
Post-germinative growth in plants is controlled by sucrose mobilization from the endosperm. Regulation of this process, however, is not fully understood. Transcriptional suppression of the rice vacuolar H + translocating pyrophosphatase (V-PPase) referred to as VPP5 led to enhanced starch content in mature grains. However, vpp5 suppressed lines displayed a slower post-germinative growth rescuable by sucrose, indicating inefficient sucrose mobilization from the endosperm. Biochemical and gene expression analyses showed a slower rate of starch to sucrose conversion and altered expression of the key starch conversion pathway genes. We hypothesized that the modulation of metabolic activities in the vpp5 lines was based on the perturbation in the homeostasis of H + and/or inorganic pyrophosphate (PPi). Concurring with this, we found enhanced levels of PPi in vpp5 germinating seeds. Metabolomic analysis of the germinating seeds at two different stages of germination revealed a slower rate of metabolism and a differential enrichment of metabolites associated with starch and sucrose metabolism in vpp5 compared to the wildtype. Notably, the yield traits of vpp5 lines were not impacted as grain numbers and grain weight of the greenhouse ripened seeds were similar to that of the wildtype. In conclusion, VPP5 encoding the endosperm-specific V-PPase regulates starch to sucrose conversion in germinating seeds, and its suppression results in a slower post-germinative growth but does not impact the reproductive development and grain yield of the plants.