The physiologies of this fungus are very different from G. zeae (Parniske, 2008). Although important for the sexual development of

G. zeae, triacylglycerides cannot move through the septal pore as lipids are stored in huge lipid bodies in the mycelia (Guenther et al., 2009). Recently, Oliver et al. (2009) proposed that fermentative intermediates (acetaldehyde, ethanol, and acetate) are generated under low oxygen stress and subsequently translocate to leaves for transpiration or recapturing of carbon sources in plants. In a similar fashion, toxic PAA pathway metabolites produced from embedded mycelia might move to aerial mycelia for recycling by ACS1 in G. zeae (Fig. S5). Expression patterns of PDC1 and ACS1 further suggest these enzymes are involved in the PAA pathway of G. zeae. Although PDC takes part in eukaryotic fermentation processes (Lehninger et al., Fluorouracil cell line 1993), PDC1 was highly expressed in both the JQ1 order aerial mycelia and embedded mycelia. However, ACS1 was only observed in the aerial mycelia, suggesting that the upstream PAA pathway intermediates generated in the embedded mycelia are subsequently translocated to the aerial mycelia (Fig.

S5). Based on the high expression of PDC1 in aerial mycelia, we hypothesize that pyruvate and/or other glycolysis intermediates are the means of carbon translocation for lipids synthesis. In this model, glucose would not be translocated to the aerial mycelia as ACS1, which is known to be repressed by glucose, was highly expressed in the aerial mycelia (Lee et al., 2011). Growth of embedded mycelia seems to be linked to the utilization of PPA pathway intermediates in G. zeae. As mentioned previously, intermediates of the PAA pathway may move to the aerial mycelia to facilitate carbon translocation. Alternatively, they could be utilized for producing energy in the embedded mycelia (Fig. S5). Transcript levels of the PDC gene are a major determinant of ethanol production in A. nidulans, underscoring the significance of ethanol fermentation in this obligate aerobic fungus (Lockington et al., 1997). PDC mediates Thiamet G conversion of pyruvate to acetaldehyde, which is reduced to ethanol

by alcohol dehydrogenase (Lehninger et al., 1993). Thus, PDC1 is likely important for energy production in the embedded mycelia, and deletion of this gene could result in reduced growth of embedded mycelia in G. zeae. In this study, we demonstrate that the PAA pathway is crucial for lipid production in the aerial mycelia (Fig. S5). Embedded mycelia appear to utilize PAA pathway intermediates via ethanol fermentation for proper growth. This is the first report that describes different physiological roles in the aerial and embedded mycelia for the same primary metabolic process in filamentous fungi. This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (2011-0000963).