Ethylene has long been regarded as the main regulator of ripening in climacteric fruits. The characterization of a few tomato mutants, unable to produce climacteric ethylene and to ripen their fruits even following treatments with exogenous ethylene, has shown that other factors also play an important role in the control of climacteric fruit ripening. In climacteric peach and tomato fruits it has been shown that, concomitant with ethylene production, increases in the amount of auxin can also be measured. In this work a genomic approach has been used in order to understand if such an auxin increase is functional to an independent role played by the hormone during ripening of the climacteric peach fruits. Besides the already known indirect activity on ripening due to its up-regulation of climacteric ethylene synthesis, it has been possible to show that auxin plays a role of its own during ripening of peaches. In fact, the hormone has shown the ability to regulate the expression of a number of different genes. Moreover, many genes involved in biosynthesis and transport and, in particular, the signalling (receptors, Auxin Response Factors and Aux/IAA) of auxin had increased expression in the mesocarp during ripening, thus strengthening the idea that this hormone is actively involved in the ripening of peaches. This study has also demonstrated the existence of an important cross-talk between auxin and ethylene, with genes in the auxin domain regulated by ethylene and genes in the ethylene domain regulated by auxin.

Notwithstanding the economic importance of non-climacteric fruits like grape and strawberry, little is known about the mechanisms that regulate their ripening. Up to now no growth regulator has emerged with a primary role similar to that played by ethylene in the ripening of the climacteric fruits. Strawberries can produce ethylene, although in limited amounts. Two cDNAs coding for enzymes of the ethylene biosynthetic pathway (i.e. FaACO1 and FaACO2), and three cDNAs encoding different ethylene receptors have been isolated. Two receptors (i.e. FaEtr1 and FaErs1) belong to the type-I while the third (i.e. FaEtr2) belongs to the type-II group. The expression of both the ACO and the receptor-encoding genes has been studied in fruits at different stages of development and in fruits treated with hormones (i.e. ethylene and the auxin analogue NAA). All the data thus obtained have been correlated to the known data about ethylene production by strawberry fruits. Interestingly, a good correlation has resulted between the expression of the genes described in this work and the data of ethylene production. In particular, similarly to what occurs during climacteric fruit ripening, there is an increased synthesis of receptors concomitant with the increased synthesis of ethylene in strawberries as well. Moreover, the receptors mostly expressed in ripening strawberries are the type-II ones, that is those with a degenerate histidine–kinase domain. Since the latter domain is thought to establish a weaker link to the CTR1 proteins, even the little ethylene produced by ripening strawberries might be sufficient to trigger ripening-related physiological responses.

Analysis of fruit surface suberization leads to the identification and characterization of AtMYB107 and AtMYB9 as positive regulators of suberin deposition in A