Tracking Alternative Versions of the Galactose Gene Network in the Genus and Their Expansion After Domestication

When grows on mixtures of glucose and galactose, galactose utilization is repressed by glucose, and induction of the gene network only occurs when glucose is exhausted. Contrary to reference alleles, alternative alleles support faster growth on galactose, thus enabling distinct galactose utilization strategies maintained by balancing selection. Here, we report on new wild populations of harboring alternative versions and, for the first time, of alternative alleles. We also show that the non-functional version found earlier in is phylogenetically related to the alternative versions, which constitutes a case of -specific maintenance of highly divergent alleles. Strains harboring the different network variants show different levels of alleviation of glucose repression and growth proficiency on galactose. We propose that domestication involved specialization toward thriving in milk from a generalist ancestor partially adapted to galactose consumption in the plant niche.