Isolation and characterization of a cDNA clone encoding an auxin influx carrier in carnation cuttings. Expression in different organs and cultivars and its relationship with cold storage

Polar auxin transport (PAT) is necessary for the formation of adventitious roots in the base of leafy stem cuttings, as has been demonstrated in several studies in which the application of PAT inhibitors strongly inhibited the rooting of cuttings. However, unlike in the case of lateral roots, there is almost no information on the molecular mechanism that controls PAT in the formation of adventitious roots. A novel cDNA encoding an auxin influx carrier has been isolated and characterized from carnation (Dianthus caryophyllus) cuttings. The full length of DcAUX1 was obtained and the deduced aminoacid sequence revealed a high degree of identity with the corresponding auxin carrier proteins from several species. The expression of this gene depended on the organ, the carnation cultivar and the length of time cuttings had been stored in a cold chamber. As a rule, expression was higher in stem than in leaves, in the basal than in the first internode and in mature than in young leaves irrespective of the cultivar and the duration of the storage. This pattern of expression agrees with the results of a previous study showing that auxin from mature leaves was essential for rooting, while exogenous auxin applied to mature leaves was polarly transported in the stem and accumulated in the basal internode (the rooting zone). Variations in the expression observed during storage (depending of the cultivar) might be related to the variation in PAT and rooting reported in previous studies.