Subdivision of light signalling networks contributes to partitioning of C4 photosynthesis.

Plants coordinate the expression of photosynthesis-related genes in response to growth and environmental changes. In species that conduct two-cell C4 photosynthesis, expression of photosynthesis genes is partitioned such that leaf mesophyll and bundle sheath cells accumulate different components of the photosynthetic pathway. The identities of the regulatory networks that facilitate this partitioning are unknown. Here we show that differences in light perception between mesophyll and bundle sheath cells facilitate differential regulation and accumulation of photosynthesis gene transcripts in the C4 crop maize (Zea mays). Key components of the photosynthesis gene regulatory network differentially accumulated between mesophyll and bundle sheath cells, indicative of differential network activity across cell types. We further show that blue light (but not red) is necessary and sufficient to activate Photosystem II assembly in mesophyll cells in etiolated maize. Finally, we demonstrate that 61% of all light-induced mesophyll and bundle sheath genes were induced only by blue light or only by red light but not both. These findings provide evidence that subdivision of light signalling networks is a component of cellular partitioning of C4 photosynthesis in maize.