Efficient Accumulation of Amylopectin and Its Molecular Mechanism in the Submerged Duckweed Mutant.

Large-scale use of fossil fuels has brought about increasingly serious problems of environmental pollution, development and utilization of renewable energy is one of the effective solutions. Duckweed has the advantages of fast growth, high starch content and no occupation of arable land, so it is a promising starchy energy plant. A new submerged duckweed mutant () with abundant starch accumulation was obtained, whose content of amylopectin accounts for 84.04% of the starch granules. Compared with the wild type (), the branching degree of starch in mutant was significantly increased by 19.6%. Chain length DP 6-12, DP 25-36 and DP > 36 of amylopectin significantly decreased, while chain length DP 13-24 significantly increased. Average chain length of wild-type and mutant starches were greater than DP 22. Moreover, the crystal structure and physical properties of starch have changed markedly in mutant. For example, the starch crystallinity of mutant was only 8.94%, while that of wild-type was 22.3%. Compared with wild type, water solubility of starch was significantly reduced by 29.42%, whereas swelling power significantly increased by 97.07% in mutant. In order to further analyze the molecular mechanism of efficient accumulation of amylopectin in mutant, metabolome and transcriptome were performed. The results showed that glucose accumulated in mutant, then degradation of starch to glucose mainly depends on α-amylase. At night, the down-regulated β-amylase gene resulted in the inhibition of starch degradation. The starch and sucrose metabolism pathways were significantly enriched. Up-regulated expression of , , , , and provide sufficient substrate for starch synthesis in mutant. From the 0H to 16H light treatment, granule-bound starch synthase () gene was inhibited, on the contrary, the starch branching enzyme () gene was induced. Differential expression of and may be an important reason for the decrease ratio of amylose/amylopectin in mutant. Taken together, our results indicated that the mutant can accumulate the amylopectin efficiently, potentially through altering the differential expression of , and . This study also provides theoretical guidance for creating crop germplasm with high amylopectin by means of synthetic biology in the future.