Addressing transcriptional heterosis

Breeders are empirically exploiting the phenomenon of heterosis, also described as hybrid vigor, for the production of high-performing hybrids in terms of productivity, quality and stress resistance. However, the genetic bases of hybrid vigor are still poorly understood. A better understanding of the genetic bases of heterosis has several extremely important implications. The aim of this work is to contribute in the understanding of the role of the modulation of gene expression in determining heterosis. At first, we adopted an approach of large-scale expression profiling, using cDNA-arrays to compare genome-wide gene expression in developing ear from two inbred lines and their corresponding highly heterotic F1 hybrid in maize. The results of this type of experiment allow us to identify hybrid-specific gene expression level in many genes and to interpret expression data in terms of dominance and additivity. However, a limitation of such an approach is the difficulties to link expression analysis to a clear heterotic phenotype. For this reason, on the basis of the results obtained, we decided to address the problem of the importance of transcriptional regulation in the establishment of heterosis in a specific metabolic pathway, for which the genes coding for key enzymes are well known and characterized. Sulfur is an essential macronutrient for plant growth, vigor and crop yield; moreover sulfur up-take is a simple pathway, which is not correlated, at root level, with photosynthesis. For the above considerations, we focused on the sulfur up-take pathway, in normal condition and S-starvation. This was carried out both in maize and Arabidopsis.