The involvement and the efficiency of the antioxidants scavenging system upon drought were examined by comparing traditional tomato landraces with respect to an industrial commercial genotype (Red Setter); for the first time, comprehensive analyses of physiological, biochemical and molecular parameters were investigated directly under real field conditions, in a typical agricultural environment of Southern Italy. The characterization of the responses upon drought evidenced peculiar changes in stomatal conductance, ascorbate peroxidase and catalase activities and expression in drought tolerant tomato landraces, with respect to the industrial genotype. An in silico analysis (promoter and co-expression study) coupled to a phylogenetic investigation of selected enzymes was performed, reinforcing the hypothesis of a basal activation of ROS scavenging machinery in the Mediterranean landraces. Thus our data suggest a constitutive increase in the expression and activities of specific enzymes involved in ROS detoxification that can play a pivotal role in the drought response shown by tomato landraces. Therefore, traditional landraces could represent an important source of useful genetic variability for the improvement of commercial varieties; their ROS detoxifying capabilities denote peculiar aspects worth being explored to better describe their specific stress tolerance.

Il pomodoro (Solanum lycopersicum L.) è tra gli ortaggi più consumati nell'Unione Europea, e costituisce una preziosa fonte alimentare di nutrienti, vitamine e antiossidanti che sono riconosciuti importanti per una dieta sana. Nel corso dei secoli, numerose varietà di pomodoro tradizionali sono state selezionate dagli agricoltori per soddisfare le esigenze locali. Per contro, le cultivar moderne sono principalmente il risultato del miglioramento genetico focalizzato sulla produttività e sulla resistenza agli stress biotici; questo ha comportato una perdita progressiva della biodiversità della coltura, ed, in generale, un peggioramento delle qualità sensoriali. Nell'ambito del programma Horizon 2020, il progetto TRADITOM "Traditional tomato varieties and cultural practices: a case for agricultural diversification with impact on food security and health of European population" (http://traditom.eu/) punta alla conservazione, caratterizzazione e valorizzazione della diversità genetica presente nelle varietà tradizionali, anche al fine di migliorare la qualità e la sostenibilità delle varietà moderne di pomodoro. A tale scopo un'ampia collezione di varietà tradizionali europee (circa 1400) è oggetto di caratterizzazione a livello genomico (mediante Genotyping by Sequencing) e fenotipico. Il nostro gruppo ha reperito circa 240 varietà italiane tradizionali di pomodoro di diversa tipologia commerciale e forma del frutto (tondino, piennolo, tondeggiante, a cuore di bue, allungata). La collezione è stata allevata secondo pratiche colturali tradizionali ed è stata caratterizzata attraverso l'impiego di descrittori qualitativi e biometrici sia a livello di pianta che di frutto, anche mediante l'utilizzo del software Tomato Analyzer. Inoltre, una parte della collezione, ascrivibile alla tipologia da serbo, è stata caratterizzata per il comportamento dei frutti in post-raccolta.

Adaptation to osmotic stress requires an extensive alteration of gene expression. Previously, we identified several genes regulated in cells adapted to polyethylene glycol (PEG). Here, the functional role of fifty of these genes was verified. Using a large-scale phenotype screening, we have identified two genes: the splicing factor IAG1 (INSENSITIVE TO ABA IN GERMINATION1) and the putative TOR-pathway component XSA1(EXTRA SENSITIVE TO ABA1). IAG1 is induced upon long-term exposure to abscisic acid (ABA) and PEG and is mainly expressed in trichomes and stomata, organs controlling transpiration. Germination analysis of plants with altered expression of IAG1 and protein interaction with the splicing factor SUA, suggest that IAG1 may be involved in premRNA splicing of effectors of ABA response leading to germination inhibition. XSA1 possibly affects pathways in ABA-mediated response to stress. XSA1 is expressed in vascular tissues and is up-regulated by long-term exposure to NaCl and ABA. xsa1-1 is ABA hypersensitive, indicating alteration in ABA biosynthesis and/or perception. Taken together, our results reveal promising mechanisms of plant adaptation to osmotic stress.

The present study was undertaken to investigate the expression, occurrence and activity of glucose 6 phosphate dehydrogenase (G6PDH - EC 1.1.1.49), the key-enzyme of the Oxidative Pentose Phosphate Pathway (OPPP), in tomato plants (Solanum lycopersicum cv. Red Setter) exposed to short- and long-term drought stress.For the first time, drought effects have been evaluated in plants under different growth conditions: in hydroponic laboratory system, and in greenhouse pots under controlled conditions; and in open field, in order to evaluate drought response in a representative agricultural environment.Interestingly, changes observed appear strictly associated to the induction of well known stress response mechanisms, such as the increase of proline synthesis, accumulation of chaperone Hsp70, and ascorbate peroxidase.Results show significant increase in total activity of G6PDH, and specifically in expression and occurrence of cytosolic isoform (cy-G6PDH) in plants grown in any cultivation system upon drought.Intriguingly, the results clearly suggest that abscissic acid (ABA) pathway and signaling cascade (protein phosphatase 2C PP2C) could be strictly related to increased G6PDH expression, occurrence and activities.We hypothesized for G6PDH a specific role as one of the main reductants' suppliers to counteract the effects of drought stress, in the light of converging evidences given by young and adult tomato plants under stress of different duration and intensity.

Tomato is a major crop in the Mediterranean basin, where the cultivation in the open field is often vulnerable to drought. In order to adapt and survive to naturally occurring cycles of drought stress and recovery, plants employ a coordinated array of physiological, biochemical, and molecular responses. Transcriptomic studies on tomato responses to drought and subsequent recovery are few in number. As the search for novel traits to improve the genetic tolerance to drought increases, a better understanding of these responses is required. To address this need we designed a study in which we induced two cycles of prolonged drought stress and a single recovery by rewatering in tomato. In order to dissect the complexity of plant responses to drought, we analyzed the physiological responses (stomatal conductance, CO2 assimilation, and chlorophyll fluorescence), abscisic acid (ABA), and proline contents. In addition to the physiological and metabolite assays, we generated transcriptomes for multiple points during the stress and recovery cycles. Cluster analysis of differentially expressed genes (DEGs) between the conditions has revealed potential novel components in stress response. The observed reduction in leaf gas exchanges and efficiency of the photosystem PSII was concomitant with a general down-regulation of genes belonging to the photosynthesis, light harvesting, and photosystem I and II category induced by drought stress. Gene ontology (GO) categories such as cell proliferation and cell cycle were also significantly enriched in the down-regulated fraction of genes upon drought stress, which may contribute to explain the observed growth reduction. Several histone variants were also repressed during drought stress, indicating that chromatin associated processes are also affected by drought. As expected, ABA accumulated after prolonged water deficit, driving the observed enrichment of stress related GOs in the up-regulated gene fractions, which included transcripts putatively involved in stomatal movements. This transcriptomic study has yielded promising candidate genes that merit further functional studies to confirm their involvement in drought tolerance and recovery. Together, our results contribute to a better understanding of the coordinated responses taking place under drought stress and recovery in adult plants of tomato.

Crop productivity is severely affected by drought and high salinity in many regions of the world and the impact of such stresses is predicted to increase drastically in the near future. To guarantee global food production to an increasing world population expected to double by 2050, the identification of genes involved in tolerance mechanisms is a key goal to develop crops better capable to handle these stresses. Adaptation to stress is a complicated process and requires an extensive alteration in gene expression. In a previous study, our group identified several genes whose expression was differentially regulated in Solanum tuberosum culture cells during gradual exposure to increasing concentrations of polyethylene glycol (PEG) (Ambrosone et al., 2013). Among these, we have selected for further studies 50 genes belonging to different functional categories. Orthologous genes in Arabidopsis thaliana were identified based on sequence homology and one homozygous knock-out line was isolated for each gene which contained a T-DNA insertion in the coding sequence. These lines were subjected to a large-scale phenotype screening in order to identify genes with a functional role in adaptation to osmotic stress. Several treatments including NaCl and Abscisic acid (ABA) were conducted and different parameters such as seed germination, root growth and plant survival in the presence of stress evaluated for each genotype. Using this strategy, we have identified 3 genes whose abolished expression has an impact on stress tolerance or ABA sensitivity. In particular, a RNA-binding protein, highly expressed in dry seed and shoot apex, showed tolerance to elevated concentration of ABA. In contrast, survival test and root growth experiments on plates allowed to identify i) a component of the TOR pathway, responsible for activating a cell-growth program in response to nutrients and stresses and ii) a putative subunit of RNA polymerase III which were hyper-sensitive to multiple stresses. We are in the process of performing a detailed functional analysis for the three selected genes using transgenic lines with the purpose of understanding their roles in plant adaptation to osmotic stress and thus contribute to future crop improvement.

Salt and drought stress severely reduce plant growth and crop productivity worldwide. The identification of genes underlying stress response and tolerance is the subject of intense research in plant biology. Through microarray analyses, we previously identified in potato (Solanum tuberosum) StRGGA, coding for an Arginine Glycine Glycine (RGG) box-containing RNA-binding protein, whose expression was specifically induced in potato cell cultures gradually exposed to osmotic stress. Here, we show that the Arabidopsis (Arabidopsis thaliana) ortholog, AtRGGA, is a functional RNA-binding protein required for a proper response to osmotic stress. AtRGGA gene expression was up-regulated in seedlings after long-term exposure to abscisic acid (ABA) and polyethylene glycol, while treatments with NaCl resulted in AtRGGA down-regulation. AtRGGA promoter analysis showed activity in several tissues, including stomata, the organs controlling transpiration. Fusion of AtRGGA with yellow fluorescent protein indicated that AtRGGA is localized in the cytoplasm and the cytoplasmic perinuclear region. In addition, the rgga knockout mutant was hypersensitive to ABA in root growth and survival tests and to salt stress during germination and at the vegetative stage. AtRGGA-overexpressing plants showed higher tolerance to ABA and salt stress on plates and in soil, accumulating lower levels of proline when exposed to drought stress. Finally, a global analysis of gene expression revealed extensive alterations in the transcriptome under salt stress, including several genes such as ASCORBATE PEROXIDASE2, GLUTATHIONE S-TRANSFERASE TAU9, and several SMALL AUXIN UPREGULATED RNA-like genes showing opposite expression behavior in transgenic and knockout plants. Taken together, our results reveal an important role of AtRGGA in the mechanisms of plant response and adaptation to stress.

In the framework of a project for the conservation of local landraces threatened with extinction, we estimated genetic relationships and true cultivar identity of 7 and 25 accessions, respectively, of eggplant and pepper landraces from the Campania Region (Southern Italy). We used an integrated approach including SSR markers (15 for eggplant and 16 for pepper) and 9 morpho-agronomic biometric traits. Out of all the tested SSR markers, 5 and 7 markers showed polymorphism between landraces in eggplant and pepper, respectively, detecting 18 alleles in eggplant and 31 alleles in pepper. These markers generated the same genetic pattern for every accession of each investigated cultivar. Despite more markers may potentially detect polymorphism, these findings suggest an elevated genetic homogeneity between landraces. The morpho-agronomic traits investigated allowed only a partial discrimination of landraces and thus call for more detailed investigation.

*) CNR-IGV Institute of Plant Genetics, UOS Portici, Via Università 133, 80055 Portici (Italy)