Dormancy without Reproduction

One of the fastest growing biomass consists of duckweeds. They cover slow moving streams and ponds because of run-offs from fertilizers. These plants grow in nearly every geographic location except in permafrost because they could not survive, when the water freezes. In climates with seasons, they have adapted to an interesting cycle of growth and dormancy. When there is shortage of nutrition in the fall or the temperature drops in the winter, they stop photosynthesis and start accumulating starch, which makes them denser causing them to sink. This switch is accompanied by a morphological change from a leaf-like structure, called frond, to turions. Because the water only freezes on top of the ponds and streams, turions can stay in the unfrozen layer at the bottom. In such a state, turions cease most metabolic activities as seeds do. Similar like seeds, they can switch back to a growth phase in spring, when the temperature rises and the water on top melts. They use starch as an energy source and float to the top, where they resume photosynthesis as fronds. Therefore, the question arises which genes are turned off and on during this cycle and whether they resemble a similar developmental program as terrestrial seed-producing plants have? We used next generation sequencing technology to examine the transcriptome of turion development triggered by exogenous ABA in Greater Duckweed, Spirodela polyrhiza, a species, whose genome has been sequenced (Nat. Commun. e3311). Interestingly, there is a resemblance of expression patterns between turions and seeds.