Giant duckweed (Spirodela polyrhiza) response to phosphorus

Baker, Stokes S., Savannah Fijal, Taj Kooner, and Mustafa Abdulrazzaq

Robust pollution monitoring methods can be used in mitigation strategies. Experiments have been initiated to determine if Spirodela polyrhiza (giant duckweed) gene expression patterns can be used to monitor the concentration of phosphorus, the limiting factor of algae growth in most aquatic ecosystems. Sterile cultures of S. polyrhiza were grown under standard laboratory conditions (40,385 ppb), under phosphorous starvation (0 ppb), and under eutrophic condition (50 ppb). Next generation sequencing experiments (i.e., RNAseq) was used to identify candidate genes that respond to phosphate starvation and ecologically relevant phosphorous concentration (50 ppb). Analysis showed that 1060 transcripts were upregulate by phosphate starvation and 1715 were down regulated. In contract, a comparison of plants growing in 50 ppb phosphorus versus 0 ppb phosphorous showed only two genes upregulated by phosphate starvation and no genes down regulated. Population growth studies of sterile cultures showed a linear response when plants were grown under phosphorous starvation (0 ppb) and
eutrophic levels (50 ppb) phosphorous. The US Environmental Protection Agency would classified aquatic environments containing 50 ppb as highly polluted. The lack of gene expression response and linear growth response of duckweed growing in sterile cultures indicate that additional component (possibly microbes) are required for efficient uptake of phosphorous by duckweed.