Department of Agronomy and Horticulture, University of Nebraska, Lincoln, Nebraska 68588, USA.
Plant Physiol. 2012 Feb;158(2):917-29. doi: 10.1104/pp.111.191163. Epub 2011 Dec 8.
Quality Protein Maize (QPM) is a hard-endosperm version of the high-lysine opaque2 (o2) maize (Zea mays) mutant, but the genes involved in modification of the soft o2 endosperm are largely unknown. Pyrophosphate-dependent fructose-6-phosphate 1-phosphotransferase (PFP) catalyzes the ATP-independent conversion of fructose-6-phosphate to fructose-1,6-bisphosphate in glycolysis. We found a large increase in transcript and protein levels of the α-regulatory subunit of PFP (PFPα) in QPM endosperm. In vitro enzyme assays showed a significant increase in forward PFP activity in developing endosperm extracts of QPM relative to the wild type and o2. An expressed retrogene version of PFPα of unknown function that was not up-regulated in QPM was also identified. The elevated expression levels of a number of ATP-requiring heat shock proteins (Hsps) in o2 endosperm are ameliorated in QPM. PFPα is also coinduced with Hsps in maize roots in response to heat, cold, and the unfolded protein response stresses. We propose that reduced ATP availability resulting from the generalized Hsp response in addition to the reduction of pyruvate, orthophosphate dikinase activity in o2 endosperm is compensated in part by increased PFP activity in QPM.
优质蛋白玉米（QPM）是高赖氨酸不透明 2 型（o2）玉米（Zea mays）突变体的硬质胚乳版本，但涉及软 o2 胚乳修饰的基因在很大程度上尚不清楚。焦磷酸依赖性果糖-6-磷酸 1-磷酸转移酶（PFP）在糖酵解中催化果糖-6-磷酸与果糖-1,6-二磷酸的非依赖 ATP 转化。我们发现 QPM 胚乳中转录物和 PFP（PFPα）α-调节亚基的水平显著增加。体外酶测定显示，与野生型和 o2 相比，QPM 发育胚乳提取物中的正向 PFP 活性显著增加。还鉴定了一种表达的未知功能的 PFPα返座基因，其在 QPM 中未上调。在 o2 胚乳中，许多需要 ATP 的热休克蛋白（Hsps）的表达水平升高，在 QPM 中得到改善。PFPα在玉米根中也与 Hsps 共同诱导，以响应热、冷和未折叠蛋白反应应激。我们提出，除了 o2 胚乳中丙酮酸、正磷酸盐二激酶活性降低外，普遍的 Hsp 反应导致的 ATP 可用性降低在 QPM 中部分得到了增加的 PFP 活性的补偿。
