Schizosaccharomyces pombeRho2p GTPase Regulates Cell Wall α-Glucan Biosynthesis through the Protein Kinase Pck2p

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Abstract
Schizosaccharomyces pombe rho1+andrho2+genes are involved in the control of cell morphogenesis, cell integrity, and polarization of the actin cytoskeleton. Although both GTPases interact with each of the twoS. pombe protein kinase C homologues, Pck1p and Pck2p, their functions are distinct from each other. It is known that Rho1p regulates (1,3)β-d-glucan synthesis both directly and through Pck2p. In this paper, we have investigated Rho2p signaling and show that pck2Δ andrho2Δ strains display similar defects with regard to cell wall integrity, indicating that they might be in the same signaling pathway. We also show that Rho2 GTPase regulates the synthesis of α-d-glucan, the other main structural polymer of the S. pombe cell wall, primarily through Pck2p. Although overexpression of rho2+in wild-type or pck1Δ cells is lethal and causes morphological alterations, actin depolarization, and an increase in α-d-glucan biosynthesis, all of these effects are suppressed in a pck2Δ strain. In addition, genetic interactions suggest that Rho2p and Pck2p are important for the regulation of Mok1p, the major (1–3)α-d-glucan synthase. Thus, a rho2Δ mutation, like pck2Δ, is synthetically lethal with mok1–664, and the mutant partially fails to localize Mok1p to the growing areas. Moreover, overexpression of mok1+inrho2Δ cells causes a lethal phenotype that is completely different from that of mok1+overexpression in wild-type cells, and the increase in α-glucan is considerably lower. Taken together, all of these results indicate the presence of a signaling pathway regulating α-glucan biosynthesis in which the Rho2p GTPase activates Pck2p, and this kinase in turn controls Mok1p.