Late acting genes in stomatal development

The stomata is involved in both the control of gas exchange and water retention in plants. It acts like a valve an is located in the leaf epidermal layers of plants. The development of stoma acts as a cell linage and is under the influence of both early and late acting genes. Following the assymetric divisions of the meristemoid that help to establish the patterning of spacing and quantity of stomata produced it is time for the late acting genes to take over. These genes help to end the growth of cells and to regulate the timing of guard cell differentiation and of their specification.

Late acting genes that end cell proliferation

In cell linages precursor cells can only divide a finite amount of times after this they must differentiate into a specialised cell. The final process in the development of the stomata is the symmetrical differentiation of the guard mother cell; this results in the two guard cells that guard the stomatal opening. In Arabidopsis three genes are known to be involved in the ending of stomata lineage cell cycling. These are the genes Myb88, FAMA and Four Lips (FLP). These encode proteins that act as transcription regulators. Mutations of Four lips results in clustering with normal and arrested stomata, this can be enhanced by mutation of the four lips paralogue Myb88. Fama encodes a protein that s a bHLH results to similar clusters. It is therefore thought that all three of these late acting genes limit the symmetrical division of genes at the end of the stomata cell lineage. Additionally FAMA is able to play a role in guard cell identity.

Late genes that act as cell cycle regulators

It is thought that genes such as Four lips and FAMA interact with the machinery that regulates the cell cycle. Unfortunately little is known about genes involved in the cell cycle machinery, this is a consequence of the lethality that is caused by many of the genes that are involved in it.

Three classes of cell cycle regulators are known to be involved in the stomatal developmental lineage.

1. Those that positively regulate the production of stomata, and also promote guard mother cell mitosis and cytokineses (eg. CDKB1)
2. Those that regulate the origins of replication (CDT1 and CDC6)
3. Those that repress the transcription factor complex E2F-DP (RBR)

It can be seen that many genes both early and late acting have an influence on the control of stomatal development; the later acting ones have a role to play in the ending of cell proliferation, cell cycling regulation and the division and differentiation of stomatal development. For more detailed information it is recommended that you read some of the papers listed.