Small RNA populations reflect the complex dialogue established between heterograft partners in grapevine.

Grafting is an ancient method that has been intensively used for the clonal propagation of vegetables and woody trees. Despite its importance in agriculture the physiological and molecular mechanisms underlying phenotypic changes of plants following grafting are still poorly understood. In the present study, we analyse the populations of small RNAs in homo and heterografts and take advantage of the sequence differences in the genomes of heterograft partners to analyse the possible exchange of small RNAs. We demonstrate that the type of grafting per se dramatically influences the small RNA populations independently of genotypes but also show genotype specific effects. In addition, we demonstrate that bilateral exchanges of small RNAs, mainly short interfering RNAs, may occur in heterograft with the preferential transfer of small RNAs from the scion to the rootstock. Altogether, the results suggest that small RNAs may have an important role in the phenotype modifications observed in heterografts.

A CURLY LEAF homologue controls both vegetative and reproductive development of tomato plants.

The Enhancer of Zeste Polycomb group proteins, which are encoded by a small gene family in Arabidopsis thaliana, participate to the control of plant development. In the tomato (Solanum lycopersicum), these proteins are encoded by three genes (SlEZ1, SlEZ2 and SlEZ3) that display specific expression profiles. Using a gene specific RNAi strategy, we demonstrate that repression of SlEZ2 correlates with a general reduction of H3K27me3 levels, indicating that SlEZ2 is part of an active PRC2 complex. Reduction of SlEZ2 gene expression impacts the vegetative development of tomato plants, consistent with SlEZ2 having retained at least some of the functions of the Arabidopsis CURLY LEAF (CLF) protein. Notwithstanding, we observed significant differences between transgenic SlEZ2 RNAi tomato plants and Arabidopsis clf mutants. First, we found that reduced SlEZ2 expression has dramatic effects on tomato fruit development and ripening, functions not described in Arabidopsis for the CLF protein. In addition, repression of SlEZ2 has no significant effect on the flowering time or the control of flower organ identity, in contrast to the Arabidopsis clf mutation. Taken together, our results are consistent with a diversification of the function of CLF orthologues in plants, and indicate that although partly conserved amongst plants, the function of EZ proteins need to be newly investigated for non-model plants because they might have been recruited to specific developmental processes.