Terminal Ear 1 and Phytochromes B1/B2 regulate maize leaf initiation independently


 Higher plants generate new leaves from shoot meristems throughout their vegetative lifespan. The tempo of leaf initiation is dynamically regulated by physiological cues, but little is known about the underlying genetic signaling pathways that coordinate this rate. Two maize (Zea mays) mutants, terminal ear1 (te1) and phytochrome B1; phytochrome B2 (phyB1; phyB2), oppositely affect leaf initiation rates and total leaf number at flowering time: te1 mutants make leaves faster whereas phyB1; phyB2 mutants make leaves slower than wild-type plants. To test whether PhyB1, PhyB2, and TE1 act in overlapping or distinct pathways to regulate leaf initiation, we crossed te1 and phyB1; phyB2, created an F2 population segregating for these three mutations, and quantified various phenotypes among the resulting genotypes, including leaf number, leaf initiation rate, plant height, leaf length, leaf width, number of juvenile leaves, stalk diameter, and dry shoot biomass. Leaf number and initiation rate in phyB1; phyB2; te1 plants fell between the extremes of the two parents, suggesting an additive genetic interaction between te1 and phyB1; phyB2 rather than epistasis. Therefore, we conclude that PhyB1, PhyB2, and TE1 likely control leaf initiation through distinct signaling pathways.