Downregulation of OsPK1, a cytosolic pyruvate kinase, by T-DNA insertion causes dwarfism and panicle enclosure in rice.

Pyruvate kinase (PK) catalyzes the final step of glycolysis. There are few reports on the role of PK in rice. Here, we identified a novel rice dwarf mutant, designated as ospk1, showing dwarfism, panicle enclosure, reduced seed set, and outgrowth of axillary buds from culm nodes. Sequence analyses of 5'-RACE indicated that a single T-DNA was inserted in the transcriptional regulatory region of OsPK1 in ospk1. Quantitative RT-PCR result showed that OsPK1 expression was decreased by approximately 90% in ospk1 compared with that in WT. Enzyme assay and transient expression in protoplasts indicated that OsPK1 encodes a cytosolic PK (PK(c)). Complementation with OsPK1 demonstrated that OsPK1 is responsible for the phenotype of ospk1. Quantitative RT-PCR and GUS staining analyses exhibited that OsPK1 was expressed mainly in leaf mesophyll cells, phloem companion cells in stems, and cortical parenchyma cells in roots. The transcriptions of four other putative enzymes involved in the glycolysis/gluconeogenesis pathway were altered in ospk1. The amount of pyruvate is decreased in ospk1. We propose that OsPK1 plays an important role through affecting the glycolytic pathway. The contents of glucose and fructose were markedly accumulated in flag leaf blade and panicle of ospk1. The sucrose level in panicle of ospk1 was decreased by approximately 84%. These findings indicated that both monosaccharide metabolism and sugar transport are altered due to the decreased expression of OsPK1. Together, these results provide new insights into the role of PK(c) in plant morphological development, especially plant height.