UBC Theses and Dissertations
The Arabidopsis MYB FOUR LIPS conditionally restricts stomatal endoreduplication Liu, Xuguang
Stomata are two-celled epidermal valves responsible for gas exchange between the shoot and the atmosphere. FOUR LIPS and MYB88 are MYB transcription factors required for correctly patterning Arabidopsis stomata. Normally the guard mother cell (GMC), a stomatal precursor cell, divides once symmetrically producing a two-celled stoma. However, when FLP function is lost via mutation, excess divisions occur which result in abnormally two (or more) stomata in direct contact. Thus FLP normally represses cell divisions allowing normal stomatal differentiation and patterning. The last division in normal stomatal development, as well as the excess divisions in flp mutants, require the activities of CYCLIN DEPENDENT KINASE B1;1 and CDKB1;2. This study reports that the loss of function of all four genes (i.e. in a flp-1 myb88 cdkb1;1 cdkb1;2 quadruple mutant) induces a novel phenotype of endoreduplicated stomata and single guard cells, which are much larger than normal. In addition, chemically blocking mitosis in the flp-1 mutant or flp-1 myb88 double mutant, as opposed to in the quadruple mutant, also induces the formation of endoreduplicated stomata and single guard cells. These data suggest that the genetic or chemical blockage of mitosis allows the loss of FLP function, which normally limits division, to instead derepress endoreplication. FLP directly targets and likely represses the expression of a series of core cell cycle genes including those that act during G1-to-S phase (such as CELL DIVISION CONTROL 6A which promotes DNA replication) and G2-to-M phase (such as CDKB1;1 which promotes mitosis). These data extend previous results showing that FLP is a developmental regulator that coordinates cell cycle and differentiation.
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