Figure 8.

A schematic model illustrating how GTL1 regulates ploidy-dependent and -independent cell growth. During late trichome development, GTL1 represses the CCS52A1 expression, resulting in a decline of the APC/C activity. Reduced APC/C activity then leads to stabilisation of active CYC/CDK complexes, which blocks further progression of the endocycle. This active repression of ploidy-dependent cell growth is the major pathway that determines final size of trichome hair cells. In addition, GTL1 is likely to act as a negative regulator of ploidy-independent cell growth by repressing the expression of other unknown genes.