An untranslated cis-element regulates the accumulation of multiple C₄ enzymes in gynandropsis gynandra mesophyll cells

C₄ photosynthesis is a complex phenotype that allows more efficient carbon capture than the ancestral C₃ pathway. In leaves of C₄ species, hundreds of transcripts increase in abundance compared with C₃ 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 C₄ Gynandropsis gynandra. Increased abundance is directed by both the promoter region and introns of the G. gynandra gene. A ninenucleotide motif located in the 59 untranslated region (UTR) is required for preferential accumulation of GUS in M cells. This element is present and functional in three additional 59 UTRs and six 39 UTRs where it determines accumulation of two isoforms of CA and pyruvate,orthophosphate dikinase in M cells. Although the GgCA4 59 UTR is sufficient to direct GUS accumulation in M cells, transcripts encoding GUS are abundant in both M and BS. Mutating the GgCA4 59 UTR abolishes enrichment of protein in M cells without affecting transcript abundance. The work identifies a mechanism that directs cellpreferential accumulation of multiple enzymes required for C₄ photosynthesis.