Synthesis of α–glucans in fission yeast spores is carried out by three alpha-glucan synthase paralogs, 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. In this work we show that three mok1 paralogs -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∆ mutant spores failed to accumulate the amylose-like spore wall-specific pigment. The absence of this material reduced the resistance of spores to different types of stress. mok12, mok13 and mok14 expression was restricted to sporulating cells and the proteins localized to the spore envelope but with different timing. In vegetative cells, β-glucans are more abundant than αglucans (55 % versus 28%). In spores, the situation was the opposite, α–glucans accounted for 46% while β-glucans were approximately 38% of the total polysaccharides. We found at least two types of α–glucan polymers; Mok12p and Mok13p were involved in the synthesis of the greater part of α–glucan in the spores envelope, a polymer that is mainly digested with mutanase (α-1,3 glucanase), while Mok14p, homologous to starch synthases, was required for the synthesis of the iodinereactive polymer that is made of α-1,4 glucose residues and susceptible to digestion with amyloglucosidase (α-1,4, and α-1,6 glucanase).