Department of Biology, Tokyo Gakugei University, Koganei-shi, Tokyo 184-8501, Japan.
Plant Cell. 2011 Aug;23(8):2895-908. doi: 10.1105/tpc.111.085415. Epub 2011 Aug 23.
Postgerminative growth of seed plants requires specialized metabolism, such as gluconeogenesis, to support heterotrophic growth of seedlings until the functional photosynthetic apparatus is established. Here, we show that the Arabidopsis thaliana fugu5 mutant, which we show to be defective in AVP1 (vacuolar H(+)-pyrophosphatase), failed to support heterotrophic growth after germination. We found that exogenous supplementation of Suc or the specific removal of the cytosolic pyrophosphate (PPi) by the heterologous expression of the cytosolic inorganic pyrophosphatase1 (IPP1) gene from budding yeast (Saccharomyces cerevisiae) rescued fugu5 phenotypes. Furthermore, compared with the wild-type and AVP1(Pro):IPP1 transgenic lines, hypocotyl elongation in the fugu5 mutant was severely compromised in the dark but recovered upon exogenous supply of Suc to the growth media. Measurements revealed that the peroxisomal β-oxidation activity, dry seed contents of storage lipids, and their mobilization were unaffected in fugu5. By contrast, fugu5 mutants contained ~2.5-fold higher PPi and ~50% less Suc than the wild type. Together, these results provide clear evidence that gluconeogenesis is inhibited due to the elevated levels of cytosolic PPi. This study demonstrates that the hydrolysis of cytosolic PPi, rather than vacuolar acidification, is the major function of AVP1/FUGU5 in planta. Plant cells optimize their metabolic function by eliminating PPi in the cytosol for efficient postembryonic heterotrophic growth.
种子植物的后萌发生长需要专门的代谢途径，例如糖异生，以支持幼苗的异养生长，直到功能性光合作用器官建立。在这里，我们展示了拟南芥 fugu5 突变体，我们证明其在 AVP1（液泡 H(+)-焦磷酸酶）中存在缺陷，在萌发后无法支持异养生长。我们发现，外源补充 Suc 或通过异源表达来自芽殖酵母（酿酒酵母）的胞质无机焦磷酸酶 1（IPP1）基因特异性去除胞质焦磷酸盐（PPi），可挽救 fugu5 表型。此外，与野生型和 AVP1(Pro):IPP1 转基因系相比，fugu5 突变体的下胚轴伸长在黑暗中受到严重限制，但在生长培养基中添加 Suc 后恢复。测量结果表明，fugu5 突变体中的过氧化物酶体 β-氧化活性、干种子中储存脂质的含量及其动员不受影响。相比之下，fugu5 突变体中的 PPi 含量高出约 2.5 倍，而 Suc 含量则比野生型低 50%。总之，这些结果清楚地表明，由于胞质 PPi 水平升高，糖异生受到抑制。这项研究表明，在植物中，AVP1/FUGU5 的主要功能是水解胞质 PPi，而不是液泡酸化。植物细胞通过消除胞质中的 PPi 来优化其代谢功能，以实现高效的后胚胎异养生长。
