Abstract
If the highly efficient C(4) photosynthesis pathway could be transferred to crops with the C(3) pathway there could be yield gains of up to 50%. It has been proposed that the multiple metabolic and developmental modifications associated with C(4) photosynthesis are underpinned by relatively few master regulators that have allowed the evolution of C(4) photosynthesis more than 60 times in flowering plants. Here we identify a component of one such regulator that consists of a pair of cis-elements located in coding sequence of multiple genes that are preferentially expressed in bundle sheath cells of C(4) leaves. These motifs represent duons as they play a dual role in coding for amino acids as well as controlling the spatial patterning of gene expression associated with the C(4) leaf. They act to repress transcription of C(4) photosynthesis genes in mesophyll cells. These duons are also present in the C(3) model Arabidopsis thaliana, and, in fact, are conserved in all land plants and even some algae that use C(3) photosynthesis. C(4) photosynthesis therefore appears to have coopted an ancient regulatory code to generate the spatial patterning of gene expression that is a hallmark of C(4) photosynthesis. This intragenic transcriptional regulatory sequence could be exploited in the engineering of efficient photosynthesis of crops.