A submerged duckweed mutant with abundant starch accumulation for bioethanol production

Duckweed is one kind of promising bioenergy plant with prominent advantages such as fast growth rate and high starch content. However, almost all previous studies focused on the natural duckweed germplasms. In this study, heavy-ion irradiation was used to establish a mutant library ofLemna aequinoctialis6002, and one mutant named submarine-1 (sub-1) was screened, which could accumulate more starch but with smaller granules. Unexpectedly, under proper external growth conditions such as poor nutritional status and insufficient growth space,sub-1mutant would sink underwater due to formation of dense tissue structure and large amount of fine starch particles with the extension of cultivation time. The starch content in the sinkingsub-1increased to over 45% (dry weight) and was 12% higher than the floatingsub-1, highlighting that submergence can be considered as a spontaneous and efficient indicator for screening of high-starch duckweed. Additionally, the saccharification efficiency of starch and ethanol yield had increased insub-1mutant compared to the wild type. Based on the unique characteristics ofsub-1mutant, a cultivation model of submerged duckweed in a simulated aquaculture pond was designed to get more starch-rich biomass, enabling effective production of renewable bioenergy.