Understanding the Physiological and Molecular Basis of Chilling Tolerance across Species of the C4 Genera Miscanthus and Spartina By

Miscanthus × giganteus is exceptional among C4 plants in its ability to acclimate to chilling temperatures (≤14 °C) and maintain a high photosynthetic capacity, in turn leading to very high productivities even in cool temperate environments. To identify mechanisms that may underlie this acclimation, RNA was isolated from Miscanthus leaves exposed to chilling and non-chilling conditions, and hybridized to Agilent microarrays developed for its close relative Zea mays. Among approximately 21000 array probes that yielded robust signals, 723 showed significant expression change in response to chilling. Approximately half of these chillingresponsive probes derived from annotated genes. Strikingly, 30 probes associated with chloroplast membrane function were all up-regulated; a feature in common with chilling tolerance in the model C3 plant species Arabidopsis thaliana. Large increases in transcripts for the psbo1 (oxygen-evolving enhancer protein 1), lhcb5 (chlorophyll a/b binding protein CP26), ndhF (NADH dehydrogenase F, chloroplast), atpA (ATP synthase alpha subunit), psbA (D1), petA (cytochrome f), and lhcb4 (chlorophyll a/b binding protein CP29), relative to house-keeping genes in M. × giganteus, were confirmed by qPCR. Chilling responses of these transcripts were studied in Z. mays and were all found to significantly decrease after 14 days of chilling treatment except in atpA and ndhF. Western blot analysis of the D1 protein and LHCII type II chlorophyll a/b binding protein showed significant increases in both proteins in M. × giganteus during chilling and significant decreases in Z. mays. As in cold tolerant C3 species, M. × giganteus grown in chilling conditions appears to counteract the loss of photosynthetic proteins and those protecting Photosystem II, which occurs in other C4 species, by increasing mRNA levels for their synthesis. 1 1 This chapter is in review by Plant Physiology under the title “Transcriptional Responses Indicate Maintenance of Photosynthetic Proteins as Key to the Exceptional Chilling Tolerance of C4 Photosynthesis in Miscanthus × giganteus” with coauthors Jay Boddu, Dafu Wang, Stephen P. Moose and Stephen P. Long.