AUXIN-CYTOKININ CROSSTALK DURING OVULE PRIMORDIA DEVELOPMENT

Coordinated action of the plant hormones auxin and cytokinins (CKs) is required for all plant developmental process. My Ph.D. project focused on the crosstalk between these two hormones involved in ovule primordia formation, and ovule number determination in Arabidopsis thaliana. Ovules develop as lateral organ from the placenta, a meristematic tissue, and once fertilized, form the seeds; therefore they propagate plant offspring and ultimately determine yield in seed-crop plants. CKs and auxin are required for ovule initiation and, CKs in particular have a positive role in the determination of ovule number. I have contribute to propose an interesting model that integrates the role of both hormones with the activity of the transcription factors MONOPTEROS (MP/ARF5), CUP SHAPE COTYLEDON 1 (CUC1) and CUC2. MP responds to auxin and activates CUC1 and CUC2. In turn the CUCs, upstream or in parallel with CKs, control expression and localization of the auxin efflux carrier PIN1, which is necessary for the ovule primordia formation. Data obtained by a transcriptomic analysis suggest that CUCs act upstream of the CKs pathway, since they regulate several genes involved in CKs catabolism and response. Moreover, we identified CYTOKININ RESPONSE FACTOR 2 (CRF2) as a key player of the auxin-cytokinin crosstalk responsible of pistil growth rate and indirectly of ovule number determination. Indeed, CRF2 is a MP direct target and it promotes PIN1 expression in response to CKs. All the results obtained have been integrated in the model that describes the molecular control of ovule primordia formation.