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Identification and characterization of target genes regulated by KNOX transcription factors in different plant species

Final Activity Report Summary - KNOX TARGET GENES (Identification and characterization of target genes regulated by KNOX transcription factors in different plant species)

Plant development is fundamentally different from developmental patterning in most animals in that very little of the plant body plan is established during embryogenesis. Embryogenesis in higher plants establishes a very simple structure that contains two stem cell populations - the shoot apical meristem (SAM) and the root meristem. Post-embryonic developmental patterning at these meristems is responsible for the morphology of the adult plant.

Plant development and growth depends on the ability of the SAM to renew itself and at the same time differentiate the different organs. Lateral organs form on the flanks of the SAM (peripheral zone) whereas the initial cells below the apical dome constitute the rib zone and contribute to the elongation of the stem. These processes are strictly regulated and coordinated by meristematic genes, by local hormonal balance and by environmental stimuli.

In plants the class 1 (KNOTTED1-like) KNOX family plays an important role in the formation and maintenance of shoot apical meristem. KNOX proteins are members of the homeodomain protein family of transcription factors that are found in all eukaryote lineages. Transcription factors are regulatory proteins that determine whether genes are transcribed or not, in other words they control when genes are switched on or off.

The present project aimed to identify the genes that are regulated (target genes) by KNOX transcription factors in order to understand how KNOX factors exert their important role in plant development. Using biochemical, molecular and bioinformatic approaches, several candidates as target genes have been identified in Arabidopsis thaliana, a plant model species for genetic studies. These genes encode for proteins that are also transcription factors involved in the signal transduction of a group of steroidal plant hormones, the brassinosteroids (BRs). BRs have been shown to be involved in numerous plant processes like cell elongation and espansion, vascular differentiation and response to light, all events that are regulated by the shoot apical meristem.