Functional characterization of peach GOLVEN-like peptides in model systems

Peach (Prunus persica L. Batsch) produces climacteric fleshy fruits; their ripening is strictly regulated and relies mainly on the action of two hormones, auxin and ethylene. A peptide belonging to GOLVEN family, CTG134, was identified some years ago as a possible candidate to regulate the interaction between the two hormones. CTG134 was previously characterized in model systems Arabidopsis thaliana and Nicotiana tabacum, where it demonstrated to influence regulative processes in which above-mentioned hormones are involved. The goal of my PhD project was to test the function of GOLVEN peptides in the regulation of peach fruit ripening. During this thesis work, genes belonging to GOLVEN family were identified, through the use of bioinformatic tools. Among them, genes transcribed during ripening stages, crucial for fruit development, were determined. Another peptide shared the CTG134 expression profile, CTG512. Both were transcribed during climacteric stage and were induced by auxin and not by ethylene. To complete its functional characterization, CTG134 was expressed in Solanum lycopersicum under the control of a fruit specific promoter. Despite no evident phenotype was detected, fruit sampling allowed to test the expression system used by reporter gene GUS, and transcriptomic analysis allowed to verify that CTG134 influences transcription of ethylene related genes possibly inducing its synthesis by inducing expression on an involved gene and increasing tissue sensitivity by partial inhibition of a receptor transcription. To perform preliminary functional characterization, CTG512 was expressed in Arabidopsis e tobacco. Siliques presented ovule and embryo abortion, correlated to transgene expression level. This phenotype is associated to auxin and ethylene action, which are necessary for ovule and embryo development. Results obtained uphold the hypothesis that GOLVEN peptides act as hormone peptides, and together with auxin and ethylene, they participate to regulate fruit developmental steps fundamental for its quality