2017年12月18日PNAS在线文章，文章报道了丙酮酸磷酸双激酶在发育胚乳中的功能。

原题目为：

Functions of maize genes encoding pyruvate phosphate dikinase in developing endosperm

影响由O2基因编码的转录因子的突变在玉米农业中很重要，因为它们可以提高玉米的营养品质。这些突变还通过降低籽粒硬度和降低农艺品质以及在食品中的应用，而造成不利影响。O2的产物对表型的贡献可能是由于调节多个靶标的结果，所以并未完全理解不理想的特征。本研究探索了一个以前没有被突变的靶标，丙酮酸磷酸双激酶（PPDK），并表明PPDK缺陷会导致与减少籽粒硬度相关的负面表型。因此，玉米改良可以通过针对个别代谢途径所决定的蛋白质和氨基酸的平衡，而不是针对多效调节子（如o2转录因子），这样或许可以更好的完成玉米改良。

Mutations affecting the transcription factor encoded by the gene o2 are important in maize agriculture because they result in improved grain nutritional quality. The mutations also cause detrimental effects by reducing kernel hardness and diminishing agronomic quality and food applications. The undesirable characteristics are not fully understood because the o2 product regulates multiple targets that could contribute to the phenotype. This study investigated one target that had not been previously mutated, pyruvate phosphate dikinase (PPDK), and showed that PPDK deficiency in isolation causes the negative phenotype associated with reduced kernel hardness. Thus, maize improvement may be better accomplished by targeting individual metabolic pathways determining protein and amino acid balance rather than pleiotropic regulators such as the o2 transcription factor.

玉米opaque2（o2）突变有利于胚乳营养品质，但由于原因尚未完全了解，会造成多种负面影响。由o2编码的bZIP 转录调节蛋白的直接靶标包括pdk1和pdk2，即丙酮酸磷酸二激酶（PPDK）。该酶可逆地将AMP，焦磷酸和磷酸烯醇式丙酮酸转化成ATP，正磷酸盐和丙酮酸盐，并在植物中发挥多种功能。在灌浆过程中，PPDK在玉米淀粉胚乳中是高度丰富的，本研究解决了PPDK在的功能。pdk1和pdk2分别通过转座子插入被灭活，并且两个基因同时被胚乳特异性RNAi 靶向。pdk2占大多数胚乳的PPDK，而pdk1则特异性的丰富于叶肉。pdk1-突变是幼苗致死的，表明C4光合作用在玉米中是必不可少的。RNAi 转基因胚乳中，无法检测到PPDK蛋白的表达和酶活性。转基因籽粒的平均重量与非转基因的相同，具有正常的胚乳淀粉和总N含量，表明PPDK不是净储存化合物合成所必需的。一个不透明的表型是由PPDK完全敲除产生的，包括玻璃质胚乳特征的丧失类似于由o2-调节的表型。在转基因胚乳中多个糖酵解中间体的浓度升高，能量电荷改变，并且淀粉粒更多但平均比正常更小。数据表明，PPDK调节胚乳代谢，潜在地通过对能量电荷的可逆调节，除了PPDK之前报道对存储蛋白基因表达的影响，揭示了o2-突变可以通过调节PPDK影响不透明表型。

Maize opaque2 (o2) mutations are beneficial for endosperm nutritional quality but cause negative pleiotropic effects for reasons that are not fully understood. Direct targets of the bZIP transcriptional regulator encoded by o2 include pdk1 and pdk2 that specify pyruvate phosphate dikinase (PPDK). This enzyme reversibly converts AMP, pyrophosphate, and phosphoenolpyruvate to ATP, orthophosphate, and pyruvate and provides diverse functions in plants. This study addressed PPDK function in maize starchy endosperm where it is highly abundant during grain fill. pdk1 and pdk2 were inactivated individually by transposon insertions, and both genes were simultaneously targeted by endosperm-specific RNAi. pdk2 accounts for the large majority of endosperm PPDK, whereas pdk1 specifies the abundant mesophyll form. The pdk1- mutation is seedling-lethal, indicating that C4 photosynthesis is essential in maize. RNAi expression in transgenic endosperm eliminated detectable PPDK protein and enzyme activity. Transgenic kernels weighed the same on average as nontransgenic siblings, with normal endosperm starch and total N contents, indicating that PPDK is not required for net storage compound synthesis. An opaque phenotype resulted from complete PPDK knockout, including loss of vitreous endosperm character similar to the phenotype conditioned by o2-. Concentrations of multiple glycolytic intermediates were elevated in transgenic endosperm, energy charge was altered, and starch granules were more numerous but smaller on average than normal. The data indicate that PPDK modulates endosperm metabolism, potentially through reversible adjustments to energy charge, and reveal that o2-mutations can affect the opaque phenotype through regulation of PPDK in addition to their previously demonstrated effects on storage protein gene expression.

每日一词

endosperm

英[ˈendəʊspɜ:m]

美[ˈendoʊspɜ:rm]

n. 胚乳;

[例句]Endosperm, cells disorganize gradually along with embryo development.

随胚的发育和生长，胚乳细胞逐渐解体。