Functional Analysis Of Rice Cellulose Synthase-Like Gene OsCSLF6 In Pi Accumulation

Phosphorus is an essential macronutrient for plant growth and development. However, the network that affects phosphate (Pi) accumulation in crops is not well established. Here, we report that OsCSLF6, a member of cellulose synthase-like family (CSLF), which is found only in grasses, is involved in Pi accumulation.Oscslf6-1 and oscslf6-2 mutant displayed similar phenotypes including reduced plant height and decrease in tiller number. Reverse transcription-PCR analysis indicated that oscslf6-1 and oscslf6-2 are knock out lines since no OsCSLF6 transcript could be detected in plants homozygous for the insertions. Complementation experiment indicates OsCSLF6 is responsible for the plant height and tiller of mutant lines. QRT-PCR analysis showed OsCSLF6 was expressed in all organs examined, with the expression being lowest in mature leaves while highest in roots, which was consistent with the GUS analysis.The oscslf6 mutants (oscslf6-1 and oscslf6-2) display Pi toxic symptoms and increased Pi accumulation in both roots and shoots under the Pi-sufficient condition, which correlate with the induced expression of Pi transporters in the knockout mutants. Consistent with the overaccumulation of Pi, significant decrease in primary root length, adventitious root length and number were observed in oscslf6 mutants as compared to the WT under Pi-sufficient condition. The plant height, tiller number, shoot and root biomass of oscslf6 mutants decreased under Pi-sufficient conditions, and this was alleviated under Pi-deficient conditions. Furthermore, leaf necrosis in the oscslf6 mutants were not seen when these plants were grown under Pi-deficient conditions. These results suggested that phosphate was the reason for the phenotypes of oscslf6 mutants.Scanning electron microscopy observations revealed that the WT sclerenchyma cell walls were heavily thickened and that the cells were nearly completely filled up at the mature stages of culms, in striking contrast to those of oscslf6-1 mutant plants. Calcofluor stains shows much stronger fluorescent signals were observed in the sclerenchyma cells, parenchyma cells and vascular bundles in the wild-type than in the oscslf6-1 mutant, demonstrating a significantly high level of cellulose in wild-type plants. These findings indicate that the oscslf6 mutant is deficient in the cell walls.In addition, sucrose (Suc) level was increased in oscslf6 mutants and the expression of sucrose synthases (OsSUS4/5) and sucrose transporters (OsSUT1/2/4/OsSweet14) genes were also induced in the shoots of oscslf6 mutants, suggesting OsCSLF6 may play a role in affecting Pi accumulation by affecting the level of carbon metabolism.