Synthesis of α-glucans in fission yeast spores is carried out by three α-glucan synthase paralogues, Mok12p, Mok13p and Mok14p

Fission yeast possesses a family of (1,3)-alpha-glucan synthase-related genes; one of them, mok1(+)/ags1(+), plays an essential function in morphogenesis during vegetative growth. Here we show that three mok1(+) paralogues -mok12(+), mok13(+) and mok14(+)- are required for sporulation to succeed, acting at different stages of the spore wall maturation process. Mutation of mok12(+) affected the efficiency of spore formation and spore viability. Deletion of mok13(+) does not affect spore viability but the spores showed reduced resistance to stress conditions. mok14 Delta mutant spores failed to accumulate the amylose-like spore wall-specific polymer. mok12(+), mok13(+) and mok14(+) expression was restricted to sporulating cells and the proteins localized to the spore envelope but with different timing. mok11(+) was also induced during the sporulation process although its deletion did not show apparently a sporulation defect. In vegetative cells, beta-glucans are more abundant than alpha-glucans (55% versus 28%). In spores, the situation was the opposite, alpha-glucans accounted for 46% while beta-glucans were approximately 38% of the total polysaccharides. We found at least two types of alpha-glucan polymers, Mok12p and Mok13p, were involved in the synthesis of the greater part of alpha-glucan in the spores envelope, a polymer that is mainly digested with alpha-1,3 glucanase, while Mok14p, homologous to starch synthases, was required for the synthesis of the iodine-reactive polymer that is made of alpha-1,4 glucose residues.