Interactive Effects of Temperature and CO2 Levels on C3 and C4 Plants

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The proposed research will improve our understanding of photosynthesis in plants affected by high rates of photorespiration occurring in warm environments. Through this work, we intend to identify new ways to improve crop performance by reducing photorespiratory limitations and thus enhancing the photosynthetic capacity of C3 plants. We will evaluate how C3 plants compensate for high rates of photorespiration by (i) studying mechanisms enhancing intracellular refixation of photorespired CO2, and (ii) the early evolution of the C4 photosynthetic pathway. In the refixation project, we will evaluate whether the formation of chloroplast sheaths around the leaf cell periphery enhances the reassimilation of photorespired CO2. We will examine if chloroplast sheath formation is inducible under low CO2 and warm temperatures promoting photorespiration, and whether species from warm environments have a better ability to recapture photorespired CO2 than those from cool climates. We will also evaluate whether plants producing chloroplast sheaths have a similar potential for photorespiratory CO2 refixation as plants engineered to release photorespired CO2 within the chloroplast. The work on the early evolution of C4 photosynthesis will evaluate the functional significance of a suite of traits termed "proto-Kranz" anatomy that appear in C3 species that are closely related to C4 plants within an evolutionary lineage. Proto-Kranz anatomy may be the first definitive stage of C4 evolution and could explain how the C4 evolutionary process is initiated. We also will generate hybrids between C3 and C4 Atriplex species in order to examine the genetic controls over the expression of C4 traits. This will be accomplished by comparing transcriptomes of hybrids with differing degrees of C4 trait expression. In addition to the discovery potential of this research, funds provided will support the training of a new generation of expertise that will help the world meet the increasing demands for food, fiber and renewable energy that photosynthesis provides.