Phytochrome B (phyB) is a photosensory receptor important for the control of plant plasticity and resource partitioning. Whether phyB is required to optimize plant biomass accumulation in agricultural crops exposed to full sunlight is unknown. Wies et al. investigated the impact of mutations in the genes that encode either phyB1 or phyB2 on plant growth and grain yield in field crops of Zea mays sown at contrasting population densities.
At high plant density, all the lines showed similar kinetics of biomass accumulation. However, compared with the wild type, the phyB1 and phyB2 mutations impaired the ability to enhance plant growth in response to the additional resources available at low plant density. This effect was largely due to a reduced leaf area (fewer cells per leaf), which compromised light interception capacity. Grain yield was reduced in phyB1 plants.
Maize plants grown in the field at relatively low densities require phyB1 and phyB2 to sense the light environment and optimize the use of the available resources. In the absence of either of these two light receptors, leaf expansion is compromised, imposing a limitation to the interception of photosynthetic radiation and growth. These observations suggest that genetic variability at the locus encoding phyB could offer a breeding target to improve crop growth capacity in the field.