The long-lived and evergreen olive tree dominates the Mediterranean landscape, representing an agroecological and cultural symbol and a genetic heritage of inestimable value. Sicily, for historical, geographical, and cultural reasons, has a very rich and distinctive olive germplasm. In this work, a large survey was conducted to discover, collect, and characterize the genetic diversity of centennial monumental olive trees from historical sites, such as the Greek Temple Valley (Agrigento), ancient gardens, or farmland present in the western part of the island. Trees were chosen based on their height, trunk, stump size, and presumed age; particularly, only olive trees with an age estimated at more than 400 years old were taken into consideration. For the morphological characterization, the leaf, fruit, and endocarp traits were analyzed. For the molecular characterization, 11 polymorphic microsatellite markers largely used for fingerprinting analysis were used. Reference cultivars were included in the analysis for comparison. Nuclear DNA was extracted from different parts of the plant (young leaves of shoots taken from the canopy and young leaves taken from suckers, which arose from the basal part of the tree) to check if the trees were grafted and to explore their diversity. Most of the monumental trees have been grafted at least one time during their long life, and some genotypes showed unique genetic profiles combined with peculiar phenotypic traits. Suckers (rootstock of the trees) showed a strict genetic relationship with an ancient monumental oleaster tree, also included in the study. “Patriarch” (original mother plants) trees of local cultivars were also identified. This research revealed a high level of the still unexplored genetic diversity of the Sicilian olive germplasm and highlighted its importance as a gene reservoir, which could support new breeding programs for the evaluation and possible selection of traits linked to putative resilience to abiotic and biotic stresses (particularly Xylella fastidiosa subsp. pauca ST53 or soil- borne diseases or insects). The results will be useful for improving the conservation process, enriching existing collections of olive genetic resources, and supporting on-farm conservation projects.

The present study aimed at identifying and mapping key genes expressed in root tissues involved in drought and salinity tolerance/resistance conserved among different fruit tree species. Twenty-six RNA-Seq samples were analyzed from six published studies in five plant species (Olea europaea, Vitis riparia Michx, Prunus mahaleb, Prunus persica, Phoenix dactylifera). This meta-analysis used a bioinformatic pipeline identifying 750 genes that were commonly modulated in three salinity studies and 683 genes that were commonly regulated among three drought studies, implying their conserved role in resistance/tolerance/response to these environmental stresses. A comparison was done on the genes that were in common among both salinity and drought resulted in 82 genes, of which 39 were commonly regulated with the same trend of expression (23 were upregulated and 16 were downregulated). Gene set enrichment and pathway analysis pointed out that pathways encoding regulation of defense response, drug transmembrane transport, and metal ion binding are general key molecular responses to these two abiotic stress responses. Furthermore, hormonal molecular crosstalk plays an essential role in the fine-tuning of plant responses to drought and salinity. Drought and salinity induced a different molecular “hormonal fingerprint”. Dehydration stress specifically enhanced multiple genes responsive to abscisic acid, gibberellin, brassinosteroids, and the ethylene-activated signaling pathway. Salt stress mostly repressed genes encoding for key enzymes in signaling proteins in auxin-, gibberellin-(gibberellin 2 oxidase 8), and abscisic acid-related pathways (aldehyde oxidase 4, abscisic acid-responsive element-binding protein 3). Abiotic stress-related genes were mapped into the chromosome to identify molecular markers usable for the improvement of these complex quantitative traits. This meta-analysis identified genes that serve as potential targets to develop cultivars with enhanced drought and salinity resistance and/or tolerance across different fruit tree crops in a biotechnological sustainable way.

Olive tree with its main final product, olive oil, is an important element of Mediterranean history, considered the emblematic fruit of a civilization. Despite its wide diffusion and economic and cultural importance, its evolutionary and phylogenetic history is still difficult to clarify. As part of the Mediterranean basin, Algeria was indicated as a secondary diversification center. However, genetic characterization studies from Maghreb area, are currently underrepresented. In this context, we characterized 119 endemic Algerian accessions by using 12 microsatellite markers with the main goal to evaluate the genetic diversity and population structure. In order to provide new insights about the history of olive diversification events in the Central-Western Mediterranean basin, we included and analyzed a sample of 103 Italian accessions from Sicily and, a set of molecular profiles of cultivars from the Central-Western Mediterranean area. The phylogenetic investigation let us to evaluate genetic relationships among Central-Mediterranean basin olive germplasm, highlight new synonymy cases to support the importance of vegetative propagation in the cultivated olive diffusion and consolidate the hypothesis of more recent admixture events occurrence. This work provided new information about Algerian germplasm biodiversity and contributed to clarify olive diversification process.

The alteration of heavy (“ON/bearing”) and light (“OFF/non-bearing”) yield in pistachio (Pistacia vera L.) has been reported to result from the abscission of inflorescence buds on high yielding trees during the summer, but the regulatory mechanisms involved in this bud abscission remain unclear. The analysis provides insights into the transcript changes between inflorescence buds on bearing and non-bearing shoots, that we indicated as “ON” and “OFF”, and shed light on the molecular mechanisms causing premature inflorescence bud abscission in the pistachio cultivar “Bianca” which can be related to the alternate bearing behavior. In this study, a transcriptome analysis was performed in inflorescence buds of “ON” and “OFF” shoots. A total of 14,330 differentially expressed genes (DEGs), most of which are involved in sugar metabolism, plant hormone pathways, secondary metabolism and oxidative stress pathway, were identified. Our results shed light on the molecular mechanisms underlying inflorescence bud abscission in pistachio and we proposed a hypothetical model behind the molecular mechanism causing this abscission in “ON” shoots. Results highlighted how changes in genes expressed in nutrient pathways (carbohydrates and mineral elements) in pistachio “ON” vs. “OFF” inflorescence buds triggers a cascade of events involving trehalose-6-phosphate and target of rapamycin (TOR) signaling, SnRK1 complex, hormones, polyamines and ROS which end, through programmed cell death and autophagy phenomena, with the abscission of inflorescence buds. This is the first study reporting gene expression profiling of the fate of “ON” and “OFF” inflorescence buds associated with the alternate bearing in the pistachio.