Deep Sequencing of the Greater Duckweed Transcriptome at the Onset of Its Dormancy

Higher plants exhibit a remarkable phenotypic plasticity to adapt to adverse environmental changes. The Greater Duckweed, Spirodela polyrhiza, as an aquatic plant, presents exceptional tolerance to cold winters through its dormant structure of turions in place of seeds. It performs active photosynthesis and reproduces vegetatively by fronds budding (growth phase) in spring and summer. When there is shortage of nutrition in the fall or the temperature drops in the winter, they switch to dormant phase of turions rich of starch that is used as energy source to germinate in the following spring.

Here, we used next generation sequencing technology to examine the transcriptome of turion development triggered by exogenous ABA. 208 genes showed more than a 4-fold increase compared with 154 down-regulated genes in developing turions. The analysis of up-regulated differential expressed genes in response to dormancy exposed an enriched interplay among various pathways: signal transduction, seed dehydration, carbohydrate and secondary metabolism, and senescence. On the other side, the genes responsible for rapid growth and biomass accumulation through DNA assembly, protein synthesis and carbon fixation are repressed. Noticeably, three members of late embryogenesis abundant protein family are exclusively expressed during turion formation. The identification and functional annotation of differentially expressed genes opens a major step towards understanding the molecular network underlying vegetative frond dormancy. Moreover, genes have been identified that could be engineered in duckweeds for practical applications easing agricultural production of food crops.