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ARS Home » Midwest Area » Urbana, Illinois » Global Change and Photosynthesis Research » Research » Publications at this Location » Publication #223549
Title: Cool C4 Photosynthesis - Pyruvate Pi dikinase expression and activity corresponds to the exceptional cold tolerance of carbon assimilation in Miscanthus x giganteus

Author
item WANG, D - UNIVERSITY OF ILLINOIS
item Portis Jr, Archie
item MOOSE, S - UNIVERSITY OF ILLINOIS
item LONG, S - UNIVERSITY OF ILLINOIS

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2008
Publication Date: 9/1/2008
Citation: Wang, D., Portis, Jr., A.R., Moose, S.P., Long, S.P. 2008. Cool C4 Photosynthesis - Pyruvate Pi dikinase expression and activity corresponds to the exceptional cold tolerance of carbon assimilation in Miscanthus x giganteus. Plant Physiology. 148(1):557-567.

Interpretive Summary: The cold-tolerant and biofuel feedstock C4 grass Miscanthus x giganteus is exceptional in its productivity in cool climates. It can maintain photosynthetically active leaves at temperatures 6°C below the minimum for Zea mays (corn), which allows it a longer growing season in cool climates. To contribute to our understanding of the basis of this difference, in this study we followed the changes in photosynthesis and two key enzymes in C4 photosynthesis, Rubisco and pyruvate phosphate dikinase, in Miscanthus and corn during a transition from warm to cold growth conditions. The studies indicated that the ability of Miscanthus to be productive and maintain photosynthetically competent leaves at low temperature as compared to corn results from maintaining the level of Rubisco and increasing the level of pyruvate phosphate dikinase in the leaves. This information will benefit scientists attempting to increase the low temperature tolerance of non-cold-tolerant C4 plants like corn.

Technical Abstract: The biofuel feedstock grass Miscanthus x giganteus is exceptional among C4 species in its high productivity in cold climates. It can maintain photosynthetically active leaves at temperatures 6°C below the minimum for Zea mays (maize), which allows it a longer growing season in cool climates. Understanding the basis for this difference between these two closely related plants may be critical in adapting maize to colder weather. When M. x giganteus and maize grown at 25ºC were transferred to 14ºC, CO2 assimilation and quantum yield of photosystem II declined by 70% and 60% respectively in the first 48hr in these two species. The decline continued in maize but arrested and then partially recovered in M. x giganteus. Within 24hr of the temperature transition the PPDK protein content per leaf area transiently declined in M. x giganteus but then steadily increased, such that after 7 days the enzyme content was a few fold higher than in leaves growing in 25 ºC, by contrast it declined throughout the chilling period in maize leaves. Rubisco levels remained constant in M. x giganteus, but declined in maize. Consistent with increased PPDK protein content, the extractable PPDK activity per leaf area (Vmax,ppdk) in cold-grown Miscanthus x giganteus leaves was higher than those in warm-grown leaves, while Vmax,ppdk was lower in cold-grown than warm-grown maize. The rate of light-activation of PPDK at low temperature was also slower in maize. The energy of activation (Ea) of extracted PPDK was lower in cold-grown than warm-grown M. x giganteus, but not in maize. The specific activities and Ea of purified recombinant PPDK from M. x giganteus and maize were similar. The increase in PPDK protein in the M. x giganteus leaves corresponded to an increase in PPDK mRNA level. These results indicate that of the two enzymes known to limit C4 photosynthesis, increase of PPDK not Rubisco content corresponds to the recovery and maintenance of photosynthetic capacity of M. x giganteus at low temperature. The results suggest a low temperature induction of either transcription of the PPDK gene or inhibition of breakdown of its mRNA in Miscanthus x giganteus, which corresponds to a large increase in PPDK protein content and activity.