Postdoctoral Research Associate University of Illinois at Urbana-Champaign Urbana, Illinois
Body of Abstract: Energycane is a tropical NADP-ME type C4 bioenergy feedstock which has highly efficient photosynthesis, excellent biomass accumulation and higher energy input/output ratio (Carvalho-Netto et al. 2019). It produces an annual crop of shoots from a perennial stem base providing a low-cost and sustainable option to growers. However, its geographical range is limited by its chilling intolerance, with photosynthesis severely impaired at ca. 17°C in common with sorghum and sugarcane.
Prior modeling and transgenic manipulations have shown pyruvate orthophosphate dikinase (PPDK), which provides phosphoenolpyruvate (PEP) to the primary carboxylase of C4 photosynthesis, is a major limitation; its cold-lability impacting low temperature photosynthesis in particular (Long & Spence 2013). The close relative, Miscanthus × giganteus, maintains photosynthesis on transfer to chilling conditions and this corresponds to large increases in leaf PPDK (Wang et al. 2008). We hypothesized that increased expression of PPDK in energycane will improve CO2 assimilation under both ambient and chilling conditions and thus increase biomass yield.
We transformed Saccharum hybrid (energycane) with PPDK gene from Sorghumbicolor. 19 out of 34 lines were expressing the transgene at various levels, and 3 lines were selected for further analyses based on net CO2 assimilation rate. When grown under ambient conditions, one of these showed an increase in light-saturate leaf CO2 uptake rate (A) of ca. 10% above the untransformed plants. Decreasing leaf temperature from 28°C to 18°C approximately halved A, but two of the over-expressors showed ca. 25% higher A than the untransformed lines. However, only one of these over-expressor lines showed a productivity increase (ca. 10%) under 28/22°C growth conditions. These results appear to support our hypothesis.