Proceedings of the LXVII Italian Society of Agricultural Genetics Annual Congress

HD-ZIP II transcription factors have been acknowledged as key regulators of plant architecture, modulating it according to environmental stimuli through the interaction with several endogenous hormones. HOMEOBOX ARABIDOPSIS THALIANA 3 (HAT3) e ARABIDOPSIS THALIANA HOMEOBOX 4 (ATHB4) have been involved, alone or redundantly with other HD-Zip II, in the development of embryo, root, SAM, leaf and flower. In all these processes, HD-ZIP II have been strongly connected with auxin homeostasis (1). Within the flower, HAT3 and ATHB4 have been shown to regulate auxin-mediated organ polarity switch during gynoecium formation (2). Here we go into detail on the role of HAT3 and ATHB4 in the flower development. All flower organs are altered in the hat3 athb4 mutant, and the expressiveness of the phenotype is highly variable. Sepals and petals show jagged edges, while stamens show an alteration in anther architecture. In the most severe cases, all organs completely loose adaxial-abaxial polarity, and form completely radialized organs, consistently with the previously shown role of HAT3 and ATHB4 in the specification of the adaxial side in leaves (2). Strikingly, we also observe alterations in organ identity, revealing a new and unsuspected function for HAT3 and ATHB4. The presence of carpelloid stuctures in sepals and the formation of staminoid petals suggest an alteration of the A-C balance in the ABC model. Crosses with marker lines show an upregulation of the C-class genes in the hat3 athb4 inflorescence. HAT3 and ATHB4 are supposed to act as transcriptional repressors through the EAR motif. We therefore analyzed the importance of the HAT3 EAR motif in the regulation of flower development by introducing into the hat3 athb4 mutant either a mutated HAT3 lacking a functional EAR motif or its wild type form. Preliminary results will be presented. In the effort to improve crops resilience to global environmental challenges, the HD-ZIP II factors set themselves as promising tools. Therefore, our laboratory has recently undertaken a translational approach on some HD-ZIP II genes in crops, namely lettuce and tomato. Particularly interesting is the HAT3/ATHB4 module, since in these crops the precursor gene has not duplicated as in Arabidopsis, therefore a single gene is the putative orthologous of both. We will present preliminary results on the orthology of the lettuce and tomato HAT3/ATHB4 gene.