FIGURE 4.

Effects of pathway mutations on O₂ requirement for culmination. Development was quantitated by counting the number of spores produced after 42–45 h, and plotting relative to the value at 21% O₂ (100%). A, strains expressing Skp1 (phyA⁻), Gn-O-Skp1 (pgtA⁻), GGn-O-Skp1 (gmd⁻), FGGn-O-Skp1 (agtA⁻), and GGFGGn-O-Skp1 (normal Ax3) were examined. 100% values were 1.6–2.3 × 10⁷ spores. B, GGn-Skp1 accumulation was recapitulated by expressing Pgt-N, which encodes the β3GalT domain of PgtA, in a pgtA⁻ strain (see Fig. 2B). agtA-null cells were complemented by overexpression of either full-length AgtA (2 clones) or AgtA-N (2 clones) under control of the discoidin promoter. Ax3 and agtA-null cells were included for reference. 100% values were 1.1–3.8 × 10⁷ spores. C, a strain overexpressing AgtA is compared with Ax3 and the agtA-null strain. 100% values were 3.0–4.4 × 10⁷ spores. Values at 2.5% O₂ were the same as at 5%, and values at 40 and 70% O₂ were very similar to those at 21% (data not shown). Trends were identical in all trials; and each result was confirmed in one or more additional trials. D, summary of data from these, and replicate trials are not shown. The average value of O₂ required for 50% maximal spore formation of each strain was obtained by averaging the differences from the 50% value for Ax3 in each same trial, and adding those values (±S.E.,*) to the average value for Ax3 across all trials. Colors correspond to traces in panels A–C. **, value for Ax3 includes its own S.E. ***, only a single trial confirming previous results (2) was performed for pgtA⁻ cells in this series.