Abstract
In Arabidopsis thaliana leaves, excessive cell enlargement is often triggered by decreased cell proliferation activity, a phenomenon that we named compensation. Compensation in fugu5 mutant is cancelled when sucrose is supplied in the growth media. Cloning of FUGU5 gene revealed that it encodes for the vacuolar H+-pyrophosphatase (H+-PPase). FUGU5 has two functions, cytosolic pyrophosphate (PPi) hydrolysis and vacuolar acidification. In this study, we attempted to analyze the two functions of FUGU5 separately. Since PPi is expected to be highly accumulated in the cytosol of fugu5 mutant cells, the cytosolic Inorganic Pyrophosphatase 1 (IPP1) gene of Saccharomyces cerevisiae was introduced to fugu5 under the control of FUGU5 own promoter. IPP1 hydrolyzes cytosolic PPi without contributing to vacuole acidification. Interestingly, our results revealed that the gross phenotype of fugu5 recovered and compensated cell enlargement was totally cancelled in the ProFUGU5::IPP1 transgenic lines. These findings convincingly demonstrated that PPi, produced during active postgerminative growth, is over-accumulated in fugu5 mutant cells and is the major cause of cell proliferation inhibition.
