Starch accounts for over 80% of the total dry weight in cereal endosperm and determines the kernel texture and nutritional quality. Amyloplasts, terminally differentiated plastids, are responsible for starch biosynthesis and storage. We screened a series of rice mutants with floury endosperm to clarify the mechanism underlying amyloplast development and starch synthesis. We identified the floury endosperm19 (flo19) mutant which shows opaque of the interior endosperm. Abnormal compound starch grains (SGs) were present in the endosperm cells of the mutant. Molecular cloning revealed that the FLO19 allele encodes a plastid-localized pyruvate dehydrogenase complex E1 component subunit α1 (ptPDC-E1-α1) that is expressed in all rice tissues. In vivo enzyme assays demonstrated that the flo19 mutant showed decreased activity of the plastidic pyruvate dehydrogenase complex. In addition, the amounts of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) were much lower in the developing flo19 mutant endosperm, suggesting that FLO19 participates in fatty acid supply for galactolipid biosynthesis in amyloplasts. FLO19 overexpression significantly increased seed size and weight, but did not affect other important agronomic traits, such as panicle length, tiller number and seed setting rate. An analysis of single nucleotide polymorphism data from a panel of rice accessions identified that the pFLO19^L haplotype was positively associated with grain length, implying a potential application in rice breeding. In summary, our study demonstrates that FLO19 is involved in galactolipid biosynthesis which is essential for amyloplast development and starch biosynthesis in rice.

中文翻译：

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质体丙酮酸脱氢酶复合物 E1 组分亚基 Alpha1 参与水稻淀粉体发育所需的半乳糖脂生物合成

淀粉占谷物胚乳总干重的 80% 以上，决定了籽粒质地和营养品质。淀粉质体是终末分化的质体，负责淀粉的生物合成和储存。我们筛选了一系列具有粉状胚乳的水稻突变体，以阐明淀粉体发育和淀粉合成的机制。我们鉴定了显示内部胚乳不透明的粉状胚乳19 ( flo19 ) 突变体。突变体的胚乳细胞中存在异常复合淀粉粒（SGs​​）。分子克隆显示，FLO19等位基因编码一个质体定位的丙酮酸脱氢酶复合物 E1 组分亚基 α1 (ptPDC-E1-α1)，该亚基在所有水稻组织中均有表达。体内酶测定表明，flo19突变体显示出质体丙酮酸脱氢酶复合物的活性降低。此外，发育中的flo19突变胚乳中单半乳糖基二酰基甘油 (MGDG) 和双半乳糖基二酰基甘油 (DGDG) 的含量要低得多，这表明FLO19参与了淀粉体中半乳糖脂生物合成的脂肪酸供应。FLO19过表达显着增加种子大小和重量，但不影响其他重要农艺性状，如穗长、分蘖数和结实率。对一组水稻种质的单核苷酸多态性数据进行分析，发现pFLO19 ^L单倍型与籽粒长度呈正相关，暗示其在水稻育种中的潜在应用。总之，我们的研究表明，FLO19参与了半乳糖脂的生物合成，这对水稻的淀粉体发育和淀粉生物合成至关重要。