Dynamics And Mechanism Of KLU-Signalling In The Control Of Plant Organ Size

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How growth in plants is controlled to generate organs with a species-specific size and shape is a fundamental question of developmental biology. The Arabidopsis KLU gene, encoding a putative cytochrome P450, controls the timing of proliferation arrest in growing primordial and thus regulates cell numbers and organ size. KLU acts in a non-cell autonomous manner by producing a mobile growth factor. Its restricted expression pattern at the periphery of organ primordia suggests a model whereby this downstream signal is used to measure the size of the growing primordium and coordinate the arrest of cell proliferation: As the KLU expressing region grows more slowly than the organ as a whole, the downstream signal will be diluted, until it can no longer sustain further proliferation beyond a given primordium size. The proposed research and training programme will focus on two main scientific objectives. Firstly, we will test feasibility of the above model by analyzing the range of action of the presumed KLU-dependent signal. To this end, we will determine whether KLU only acts locally in growing organs or whether its range of action is long enough to be able to coordinate growth throughout the shoot. 'Genetic grafting' to combine varying proportions of klu mutant and wild-type tissue in one plant will be used to answer this question. Secondly, we will use reverse genetics based on previous microarray analyses to isolate additional genes required for KLU-dependent growth signalling. These complementary approaches will provide important insight into the mode of action of this novel growth signalling system in organ size control.

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