In vitro culture conditions and OeARF and OeH3 expressions modulate adventitious root formation from oleaster (Olea europaea L. subsp. europaea var. sylvestris) cuttings.

Olea europaea L. subsp. europaea var. sylvestris, also named oleaster, is the wild form of olive and it is used as rootstock and pollen donor for many cultivated varieties. An efficient procedure for in vitro propagation of oleaster was established in this study. A zeatin concentration of 2.5 mg/L was effective to induce an appreciable vegetative growth. Also high rooting efficiency was obtained by using a short IBA pulse, followed by two different IBA concentrations in the culture medium. With the aim to enlarge knowledge on the molecular aspects of adventitious rooting, we also evaluated the transcriptional modulation of an ARFs member and HISTONE H3 genes, involved in auxin signaling and cell replication, respectively, during the root induction phase of cuttings. The obtained results suggest that the selected genes, as markers of the induction phase, could be very useful for setting up efficient culture conditions along the rooting process, thus increasing micropropagation efficiency.

Role of geranylgeranyl reductase gene in organ development and stress response in olive (Olea europaea) plants.

The NADPH-dependent geranylgeranyl reductase gene (OeCHLP) was characterised in olive (Olea europaea L.). OeCHLP catalyses the formation of carbon double bonds in the phytolic side chain of chlorophyll, tocopherols and plastoquinones and, therefore, is involved in metabolic pathways related to plant productivity and stress response, besides to nutritional value of its products. The nuclear OeCHLP encodes a deduced product of 51 kDa, which harbours a transit peptide for cytoplasm-to-chloroplast transport and a nicotinamide binding domain. Two estimated identical copies of gene are harboured per haploid genome of the cv. 'Carolea' used in the present study. Levels and cytological pattern of OeCHLP transcription were investigated by quantitative RT-PCR and in situ hybridisation. In line with the presence of ubiquitous tocopherols and/or chlorophyll, OeCHLP transcripts were present in various organs of plants. In leaves and fruits at different developmental stages, OeCHLP was differentially expressed in relation to their morpho-physiological features. An early and transient enhancement of gene transcription was detected in leaves of different age exposed to cold treatment (4°C), as well as in fruits mechanically wounded. Moreover, OeCHLP transcripts locally increased in specific cell domains of fruits severely damaged by the pathogen Bactrocera olea. Combined, these data show that OeCHLP expression early responds to biotic and abiotic stressful factors. Levels of tocopherols also increased in leaves exposed to cold conditions and fruits severely damaged by pathogen. We suggest that gene activity under stress condition could be related to tocopherol action.