Abstract

The C4 pathway has evolved in at least 66 lineages of angiosperms. Typically, the activity of enzymes associated with the core pathway are restricted to either mesophyll (M) or bundle sheath (BS) cells, and the mechanisms generating this cell specificity are beginning to be understood for several genes. However, there are very few examples in which the same mechanism has been shown to underlie cell specificity of the multiple genes required for C4 photosynthesis. We recently showed that the untranslated regions (UTRs) of both the pyruvate,orthophosphate dikinase (PPDK) and ß-carbonic anhydrase 4 (CA4) are sufficient to direct M-specificity in C4 Cleome gynandra (Kajala et al 2012, Plant J. 69, 47–56). I now show that the same mechanism is responsible for M-specific accumulation of PPDK and CA4 transcripts as well as CA2 . Deletion analysis, computational prediction and site directed mutagenesis identified a 9-nucleotide motif in both the 5’ and 3’ UTRs of PPDK and CA2 /4 that is necessary for M-specificity. In addition, disruption of the secondary structure of UTRs also abolishes M-specificity. A hypothesis for the regulation of these transcripts by UTR binding trans-acting factors at the translation initiation complex is proposed.