An Untranslated cis-Element Regulates the Accumulation of Multiple C4 Enzymes in Gynandropsis gynandra Mesophyll Cells

C 4 photosynthesis is a complex phenotype that allows more efficient carbon capture than the ancestral C 3 pathway. In leaves of C 4 species, hundreds of transcripts increase in abundance compared with C 3 relatives and become restricted to mesophyll (M) or bundle sheath (BS) cells. However, no mechanism has been reported that regulates the compartmentation of multiple enzymes in M or BS cells. We examined mechanisms regulating CARBONIC ANHYDRASE4 ( CA4 ) in C 4 Gynandropsis gynandra . Increased abundance is directed by both the promoter region and introns of the G. gynandra gene. A nine-nucleotide motif located in the 5′ untranslated region (UTR) is required for preferential accumulation of GUS in M cells. This element is present and functional in three additional 5′ UTRs and six 3′ UTRs where it determines accumulation of two isoforms of CA and pyruvate,orthophosphate dikinase in M cells. Although the GgCA4 5′ UTR is sufficient to direct GUS accumulation in M cells, transcripts encoding GUS are abundant in both M and BS. Mutating the GgCA4 5′ UTR abolishes enrichment of protein in M cells without affecting transcript abundance. The work identifies a mechanism that directs cell-preferential accumulation of multiple enzymes required for C 4 photosynthesis.