Crosslinks in the cell wall of budding yeast control morphogenesis at the mother-bud neck.

Previous work has shown that, in cla4Δ cells of budding yeast, where septin ring organization is compromised, the chitin ring at the mother-daughter neck becomes essential for prevention of neck widening and for cytokinesis. Here, we show that it is not the chitin ring per se, but its linkage to β(1-3)glucan that is required for control of neck growth. When in a cla4Δ background, crh1Δ crh2Δ mutants, in which the chitin ring is not connected to β(1-3)glucan, grew very slowly and showed wide and growing necks, elongated buds and swollen cells with large vacuoles. A similar behavior was elicited by inhibition of the Crh proteins. This aberrant morphology matched that of cla4Δ chs3Δ cells, which have no chitin at the neck. Thus, this is a clear case in which a specific chemical bond between two substances, chitin and glucan, is essential for the control of morphogenesis. This defines a new paradigm, in which chemistry regulates growth.