Duckweed: a starch-hyperaccumulating plant under cultivation with a combination of nutrient limitation and elevated CO2

Ling Guo ^1,2 Yang Fang ¹ Songhu Wang ¹ Yao Xiao ³ Ding Yanqiang ¹ Yanling Jin ¹ Xueping Tian ¹ Du Anping ¹ Zhihua Liao ⁴ He Kaize ¹ Shuang Chen ¹ Yonggui Zhao ⁵ Li Tan ¹ Zhuolin Yi ¹ Yuqing Che ¹ Lanchai Chen ¹ Jinmeng Li ¹ Leyi Zhao ⁶ Peng Zhang ⁷ Zhengbiao Gu ⁸ Fangyuan Zhang ⁴ Yan Hong ⁸ Qing Zhang ⁹ Hai Zhao ^1*

• ¹ Chengdu Institute of Biology, Chinese Academy of Sciences (CAS), Chengdu, Sichuan Province, China
• ² The Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan, China
• ³ Sichuan University of Science and Engineering, Zigong, Sichuan, China
• ⁴ Southwest University, Chongqing, Chongqing Municipality, China
• ⁵ Yunnan University, Kunming, Yunnan Province, China
• ⁶ Pitzer College, Claremont, California, United States
• ⁷ National Key Laboratory of Plant Molecular Genetics, Center for Excellence in Molecular Plant Sciences (CAS), Shanghai, China
• ⁸ School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu Province, China
• ⁹ College of Food and Bioengineering, Xihua University, Chengdu, Sichuan Province, China

The increasing global demand for starch has created an urgent need to identify more efficient and sustainable production methods. However, traditional starch sources, such as crop-based options, experience significant bottlenecks due to limitations in land use, water consumption, and the impacts of climate change. Therefore, there is a pressing need to explore and develop new sources of starch. Here, we report a new technology that efficiently produces starch from duckweed. Although Landoltia punctata exhibits dramatic gene family contraction, its starch content and productivity reached 72.2% (dry basis) and 10.4 g m -2 d -1 , respectively, in 10 days, equivalent to a yield of 38.0 t ha -1 y -1 , under nutrient limitation treatment with elevated CO2 levels. We also examined the mechanism of high starch accumulation in duckweed. This phenomenon is associated with the regulation of DNA methylation and transcription factors as well as the significantly upregulated transcription levels and the increased activities of key enzymes involved in starch biosynthesis. Moreover, while nitrogen redistribution was increased, sucrose biosynthesis and transportation and lignocellulose biosynthesis were reduced. These alterations led to a reduction in lignocellulose and protein contents and ultimately an increase in the accumulation of starch in the chloroplasts. This work demonstrates the potential of duckweed as a highly efficient starch producer.