Wu Hao, Clay Kasi, Thompson Stephanie S, Hennen-Bierwagen Tracie A, Andrews Bethany J, Zechmann Bernd, Gibbon Bryan C
Department of Biology, Baylor University, Waco, Texas, 76798, United States of America.
Iowa State University, Department of Biochemistry, Biophysics, and Molecular Biology, Ames, Iowa, 50011, United States of America.
PLoS One. 2015 Jun 26;10(6):e0130856. doi: 10.1371/journal.pone.0130856. eCollection 2015.
The opaque-2 (o2) mutation of maize increases lysine content, but the low seed density and soft texture of this type of mutant are undesirable. Lines with modifiers of the soft kernel phenotype (mo2) called "Quality Protein Maize" (QPM) have high lysine and kernel phenotypes similar to normal maize. Prior research indicated that the formation of vitreous endosperm in QPM might involve changes in starch granule structure. In this study, we focused on analysis of two starch biosynthetic enzymes that may influence kernel vitreousness. Analysis of recombinant inbred lines derived from a cross of W64Ao2 and K0326Y revealed that pullulanase activity had significant positive correlation with kernel vitreousness. We also found that decreased Starch Synthase III abundance may decrease the pullulanase activity and average glucan chain length given the same Zpu1 genotype. Therefore, Starch Synthase III could indirectly influence the kernel vitreousness by affecting pullulanase activity and coordinating with pullulanase to alter the glucan chain length distribution of amylopectin, resulting in different starch structural properties. The glucan chain length distribution had strong positive correlation with the polydispersity index of glucan chains, which was positively associated with the kernel vitreousness based on nonlinear regression analysis. Therefore, we propose that pullulanase and Starch Synthase III are two important factors responsible for the formation of the vitreous phenotype of QPM endosperms.
玉米的不透明2（o2）突变可增加赖氨酸含量，但这类突变体种子密度低且质地软，不尽人意。带有软质胚乳表型修饰基因（mo2）的品系被称为“优质蛋白玉米”（QPM），其赖氨酸含量高且胚乳表型与普通玉米相似。先前的研究表明，QPM中玻璃质胚乳的形成可能涉及淀粉颗粒结构的变化。在本研究中，我们着重分析了两种可能影响胚乳玻璃质化的淀粉生物合成酶。对W64Ao2和K0326Y杂交所得重组自交系的分析表明，支链淀粉酶活性与胚乳玻璃质化呈显著正相关。我们还发现，在相同的Zpu1基因型条件下，淀粉合酶III丰度降低可能会降低支链淀粉酶活性和葡聚糖平均链长。因此，淀粉合酶III可通过影响支链淀粉酶活性并与支链淀粉酶协同作用来改变支链淀粉的葡聚糖链长分布，从而间接影响胚乳玻璃质化，导致淀粉结构特性不同。葡聚糖链长分布与葡聚糖链的多分散指数呈强正相关，基于非线性回归分析，该指数与胚乳玻璃质化呈正相关。因此，我们认为支链淀粉酶和淀粉合酶III是导致QPM胚乳玻璃质表型形成的两个重要因素。
