An Increase In Expression Of Pyruvate Pi Dikinase Corresponds To Cold-Tolerant C4 Photosynthesis Of Miscanthus X Giganteus

Abstract

Miscanthus x giganteus is exceptional among C4 plants in its ability to produce leaves and photosynthesize at low temperature. Understanding how this is achieved is critical to adapting other C4 crops like Z. mays to colder climates or allowing them to make use of solar radiation over a longer period of the year. Transgenic analysis of C4 plants has shown that two enzymes share control and are limiting to the light-saturated rate of photosynthe- sis: Rubisco and Pyruvate Pi Dikinase (PPDK). When maize and Miscanthus are transferred from 25°C to 14°C, both light-saturated photosynthetic rate and maximum quantum yield declined by 60–70% in both species in the first 48 h. In maize, it continued to decline in these existing leaves over the next 7 days, but recovered in Miscanthus. What changes underlie this difference? Within 48-h of the temperature transition the PPDK protein con- tent transiently declined in Miscanthus but then steadily increased a few fold over the next days, while it declined in the maize leaves. Rubisco lev- els remained constant in Miscanthus, but declined in maize. Semi-quantitative PCR showed that the increase in PPDK protein in the Miscanthus leaves corresponded to a large increase in mRNA level for PPDK. In addition, the activation energy (Ea) of PPDK is lower in cold-grown than warm- grown Miscanthus, while it is opposite in maize. The results suggest that increase of PPDK and not Rubisco corresponds to the recovery of photosyn- thetic capacity during low temperature exposure of Miscanthus x giganteus.