Plastidic pyruvate dehydrogenase complex E1 component subunit Alpha1 is involved in galactolipid biosynthesis required for amyloplast development in rice

Abstract

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 a1 (ptPDC-E1-a1) 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.

Genome-Wide Association Study of Rice Grain Shape and Chalkiness in a Worldwide Collection of Xian Accessions

“…In this study, one promising gene located in the QTL for grain weight was also identified. For qTGW4.2 , LOC_Os04g02900 ( FLO19 ) [ 39 ] encodes a pyruvate dehydrogenase complex E1-alpha subunit involved in the biosynthesis of galactolipids, which is required for the development of amyloplasts. The mutation of this gene significantly decreased the pyruvate dehydrogenase complex enzyme activity, accompanied by a significant decrease in total galactolipid content, which led to the abnormal development of amyloplasts, impaired starch synthesis and ultimately seriously affected rice yield and quality.…”

Triacylglycerol lipase, OsSG34, plays an important role in grain shape and appearance quality in rice

“…Galactolipid as one kind of lipids is essential for amyloplast development. Mutations of ENLARGED STARCH GRAIN1 (ESG1), FLOURY SHRUNKEN ENDOSPERM1 (FSE1), and FLOURY ENDOSPERM19 (FLO19) caused defective galactolipid synthesis, thereby showing a floury endosperm phenotype (Lei et al., 2022; Long et al., 2018; Wang, Ren, et al., 2021; Wang, Zhang, et al., 2021). The previous papers have presented the change in lipid and carbohydrates resulted in the chalkiness and floury endosperm in rice.…”

Understanding the regulation of cereal grain filling: The way forward

“…Developing endosperm of the flo19 mutant contains altered membrane lipid contents, which might affect starch biosynthesis and starch grain development. Overexpressing FLO19 increased grain size and grain yield in rice, suggesting that this gene could be valuable for rice breeding (Lei et al, 2022).…”