DAMOKLUS

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

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 Obiettivo del progetto (Objective)

'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 primordia 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 three scientific objectives. Firstly, we will test the above model by analyzing in detail the range and dynamics of KLU signalling in growing organs. This will be done using a specific KLU-responsive reporter gene based on the analysis of identified KLU-responsive promoters. Secondly, 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. Thirdly, we will screen for mutants in additional genes required to generate, perceive and transduce the KLU-dependent growth signal, using a luciferase-based reporter system. These complementary approaches will provide important insight into the dynamics and molecular mechanism of KLU-dependent signalling in size control. Conceptually, they will underpin detailed comparisons between the mechanisms of size regulation in animals and plants to uncover possible common principles despite different molecular implementations.'

Introduzione (Teaser)

Biology is still searching for answers to how molecular and genetic mechanisms regulate plant growth. Studies of gene expression are helping to chip away at the unknown.

Descrizione progetto (Article)

Developmental biologists are making strides in learning more about how plant growth is directed in such as a way as to eventually generate organs with a species-specific size and shape. The Arabidopsis KLU gene that encodes the cytochrome P450 (CYP) enzyme is known to regulate cell numbers and organ size. Researchers believe this contributes to growth signalling on the outer edges of plant organs; the question here is how far this signal can go.

The 'Dynamics and mechanism of KLU-signalling in the control of plant organ size' (Damoklus) project aimed to study this mobile growth factor and offer greater insight into the coordination of growth in plants.

In efforts to determine the range of action of the presumed growth signal, researchers generated chimaeric plants consisting of wild-type tissue with and mutant tissue without the CYP enzyme activity. Results showed that as well as promoting growth, the signal also coordinates growth of organs within one flower and of the different flowers within one flower head (inflorescence).

Damoklus then worked to reduce the activity of other CYP genes in plants in order to determine if other played a role in controlling growth. This action resulted in some plants having smaller leaves and flowers and thinner stems, just like plants that don't have the original CYP gene. Project partners concluded that these CYP genes act to generate the mobile growth signal.

Experiments to identify any other genes taking part in generating or perceiving the signal revealed one mutant line that could not activate the reporter gene. In these plants, even smaller organs were formed than in plants lacking the CYP gene.

The Damoklus project was able to demonstrate that the growth signal is active throughout the whole inflorescence. This suggests that it is responsible for coordinating growth of the different organs and by extension ensures the symmetry of flowers, which is important for pollination.

The successes achieved in the project can potentially lead to enhanced methods of manipulating organ growth in economically relevant crops.