Defects in Cell Wall Differentiation of the Arabidopsis Mutant rol1-2 Is Dependent on Cyclin-Dependent Kinase CDK8

Plant cells are encapsulated by cell walls whose properties largely determine cell growth. We have previously identified the rol1-2 mutant, which shows defects in seedling root and shoot development. rol1-2 is affected in the Rhamnose synthase 1 (RHM1) and shows alterations in the structures of Rhamnogalacturonan I (RG I) and RG II, two rhamnose-containing pectins. The data presented here shows that root tissue of the rol1-2 mutant fails to properly differentiate the cell wall in cell corners and accumulates excessive amounts of callose, both of which likely alter the physical properties of cells. A surr (suppressor of the rol1-2 root developmental defect) mutant was identified that alleviates the cell growth defects in rol1-2. The cell wall differentiation defect is re-established in the rol1-2 surr mutant and callose accumulation is reduced compared to rol1-2. The surr mutation is an allele of the cyclin-dependent kinase 8 (CDK8), which encodes a component of the mediator complex that influences processes central to plant growth and development. Together, the identification of the surr mutant suggests that changes in cell wall composition and turnover in the rol1-2 mutant have a significant impact on cell growth and reveals a function of CDK8 in cell wall architecture and composition.