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Title: EXPRESSION OF C4 PHOTOSYNTHETIC ENZYMES IN OAT-MAIZE CHROMOSOME ADDITION LINES

Author
item KOWLES, RICHARD - UNIVERSITY OF MINNESOTA
item WALCH, MATTHEW - UNIVERSITY OF MINNESOTA
item MINNERATH, JEANNE - UNIVERSITY OF MINNESOTA
item BERNACCHI, C - CTR. ATMOSPHERIC SCI., IL
item STEC, ADRIAN - UNIVERSITY OF MINNESOTA
item Rines, Howard
item PHILLIPS, RONALD - UNIVERSITY OF MINNESOTA

Submitted to: Maydica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2008
Publication Date: 6/1/2008
Citation: Kowles, R.V., Walch, M.D., Minnerath, J.M., Bernacchi, C.J., Stec, A.O., Rines, H.W., Phillips, R.L. 2008. Expression of C4 photosynthetic enzymes in oat-maize chromosome addition lines. Maydica. 53:69-78.

Interpretive Summary: Oat is a highly nutritious cereal grain that also can provide favorable environmental effects when included as part of a crop rotation system by farmers. However, the amount of land planted to oat is limited in the U.S. because oat tends to be less productive and more sensitive to heat stress than corn, the major U.S. cereal crop. Corn, along with a limited number of other plant species, is characterized by a special type of photosynthesis, termed C4 photosynthesis. This C4 type of the process by which plants use sunlight energy to convert carbon dioxide to carbohydrates is more efficient and less sensitive to heat stress than the more common C3 type of photosynthesis, as is present in oat. C4 plant species have a complex set of enzymes and tissue structure components that enable C4 photosynthesis; these are lacking in C3 plant species. We used a novel set of modified oat plants in which part of the genetic material of corn had been added to oat to see if some of the components necessary for C4 photosynthesis had also been introduced into these oat plants. Using molecular and biochemical detection methods we were able to show that modified oat plants with one specific portion of the genetic material of corn, specifically one of the ten chromosomes of corn, had present one of the key C4 components, the enzyme C4-PEP carboxylase. A different modified oat line containing a different corn chromosome had present another C4 enzyme, one referred to as PPdK. The demonstration that these components of C4 photosynthesis can be transferred from corn into oat and be active provides the basis for a series of studies by plant researchers to understand better the necessary components and interactions of the C4 mechanism. Such studies may one day make possible adding features of C4 photosynthesis with accompanying increased productivity and heat tolerance to C3 crop species such as oat.

Technical Abstract: Oat-maize addition lines have been successfully generated, and they are available for every maize chromosome, 1 through 10. Addition lines are oat plants (C3 photosynthesis) that include one or more chromosomes from maize (C4 photosynthesis). These oat-maize addition lines and derivative radiation hybrid lines may be useful to determine the extent to which individual maize chromosomes contribute to C4 photosynthesis and for the identification of the precise chromosomal regions involved in C4 photosynthesis. Investigations have been conducted that focused on the expression of two C4 enzymes in these oat-maize addition lines. Northern blots showed C4-associated phosphoenolpyruvate carboxylase (PEPc) mRNA expression in the oat-maize addition line containing maize chromosome 9 and C4-associated pyruvate orthophosphate dikinase (PPDK) mRNA expression in the oat-maize addition line containing chromosome 6. Immunoblotting with polyclonal antibodies against PEPc and PPDK in leaf protein extracts further showed the translation of the detected mRNA and confirmed the location of the C4-associated PEPc gene to chromosome 9 and the gene for C4-associated PPDK to chromosome 6. Indirect immunocytological tests on microtomed leaf tissue using monoclonal antibodies against PEPc and PPDK showed gene expression for PEPc in mesophyll cells of the oat-maize chromosome 9 line and PPDK in mesophyll cells of the oat-maize chromosome 6 line. Assays with leaf extracts showed highly elevated PEPc and PPDK enzyme activities in the oat-maize chromosome 9 and 6 lines, respectively. These results demonstrate that oat plants containing an alien maize chromosome can exhibit enzymatic C4 photosynthetic characteristics.