The invention relates to a method for producing a C.sub.4-type plant having a modified carbon metabolism, comprising the following steps: an expression cassette, which comprises a nucleotide sequence that codes for a phosphoenolpyruvate carboxylase (PEPC), is introduced into at least one cell of plant C.sub.4; the cell thus transformed is cultivated in such a way as to regenerate a C.sub.4 plant containing said expression cassette in the genome thereof.