Fig. 3.

Epistasis analysis and the commitment timing of hetP, asl1930, alr2902, and alr3234 mutant strains. (A) Plots of the percentage of heterocysts formed as a function of time after nitrogen stepdown. For simplicity, one representative curve is shown from each epistasis group. The full dataset can be seen in SI Appendix, Table S1. Wild type, ΔhetP (UHM158), single-mutant representative (Δasl1930 UHM295), double-mutant representative (ΔhetP Δasl1930 UHM288), triple-mutant representative (ΔhetP Δasl1930 Δalr2902 UHM282), triple homolog mutant Δasl1930 Δalr2902 Δalr3234 (UHM282), and quadruple mutant ΔhetP Δasl1930 Δalr2902 Δalr3234 (UHM333). Error bars represent the SD of three replicates. (B) Dynamics of commitment to a heterocyst fate. Cultures were stepped down to media lacking combined nitrogen to induce heterocyst development and then harvested at the time points indicated and supplemented with ammonia. Each data point represents the percent heterocyst accumulation 24–48 h after supplementation with ammonia. Error bars represent the SD for three replicates. For simplicity, one representative of each commitment phenotype is graphed. The full dataset can be seen in SI Appendix, Table S1. Strains depicted are as follows: wild type, ΔhetP (UHM158), Δalr3234 (UHM336), and ΔhetP Δasl1930 Δalr2902 Δalr3234 (UHM333).