Maria Cammareri

Enhanced triterpene saponin biosynthesis and root nodulation in transgenic barrel medic (Medicago truncatula Gaertn.) expressing a novel β‐amyrin synthase (AsOXA1) gene

Triterpene saponins are a group of bioactive compounds abundant in the genus Medicago, and have been studied extensively for their biological and pharmacological properties. In this article, we evaluated the effects of the ectopic expression of AsOXA1 cDNA from Aster sedifolius on the production of triterpene saponins in barrel medic (Medicago truncatula Gaertn.). AsOXA1 cDNA encodes beta-amyrin synthase, a key enzyme involved in triterpene saponin biosynthesis. One of the four transgenic lines expressing AsOXA1 accumulated significantly larger amounts of some triterpenic compounds in leaf and root than did control plants. In particular, the leaf exhibited significantly higher levels of bayogenin, medicagenic acid and zanhic acid. The amounts of medicagenic acid and zanhic acid, which represent the core of the M. truncatula leaf saponins, were 1.7 and 2.1 times higher, respectively, than the amounts extracted from the control line. In root, the production of bayogenin, hederagenin, soyasapogenol E and 2beta-hydroxyoleanolic acid was increased significantly. The increase in the total amounts of triterpenic compounds observed in the leaves of transgenic lines correlated with the AsOXA1 expression level. Interestingly, the plants expressing AsOXA1 showed, under different growth conditions, improved nodulation when compared with the control line. Nodulation enhancement was also accompanied by a significant change in the soyasapogenol B content. Our results indicate that the ectopic expression of AsOXA1 in barrel medic leads to a greater accumulation of triterpene saponins and enhanced root nodulation.

Resolution by recombination: breaking up Solanum pennellii introgressions

Quantitative trait locus (QTL) genetics retains an important role in the study of biological and agronomic processes; however, its genetic resolution is often comparatively low. Community-based strategies are thus required to address this issue. Here we detail such a strategy wherein the widely used Solanum pennellii introgression lines (ILs) in the genetic background of the cultivated tomato (Solanum lycopersicum) are broken up into molecular marker-defined sublines as a community resource for map-based cloning.

Solanum sect. Lycopersicon

In this review, we examine the plant group Solanum sect. Lycopersicon – a clade of 13 species, including the domesticated tomato (Solanum lycopersicum L.) and its wild relatives – along with four allied species in the immediate outgroups Solanum sects. Juglandifolia and Lycopersicoides. We summarize the geographic distribution and morphological characters of these plant groups, describing their evolutionary relationships in the context of a new taxonomic revision at the species level of all these groups. We provide an overview of the role that wild tomato species have played in the development of cytogenetic stocks, in classical and molecular genetic studies as well as in crop improvement through traditional and advanced tools. We discuss how the very narrow genetic basis of cultivated tomato germplasm has forced tomato geneticists and breeders to rely on the wealth of genetic variation present in the wild relatives to address the many breeding challenges. The numerous molecular mapping studies conducted using interspecific crosses have clearly demonstrated that the breeding value of exotic (wild) tomato germplasm goes far beyond its phenotype. These studies also show that we are still far from being able to fully exploit the breeding potential of the thousands of accessions stored in seed banks around the world, in addition to those that may still be found in natural habitats. Over the past decades, tomato breeders have been at the forefront of establishing new principles for crop breeding based on the use of wild species to improve modern cultivars. In this respect, among all model systems, the wild and domesticated species of the tomato clade have pioneered development of novel populations such as “exotic libraries.” These genetic resources, combined with the increasing knowledge deriving from the many “omics” tools, including the tomato genome sequence, are expected to further improve the efficiency with which wild tomato relatives will contribute to the improvement of this important crop.

Elucidation of meiotic nuclear restitution mechanisms in potato through analysis of microtubular cytoskeleton

Organization and rearrangements of microtubular cytoskeleton (MTs) during microsporogenesis are determined in ‘historical’ potato genotypes producing 2n pollen following different meiotic nuclear restitution mechanisms (‘parallel spindles’, ‘fused spindles’, ‘premature cytokinesis’). The scope of the investigation is to assess the abnormalities in MT cytoskeleton and their relationships to 2n pollen formation. The genotypes of Solanum used for MT immunofluorescence in this study are diploid interspecific hybrids (2n=2x=24) coming from Wisconsin (USA)and Wageningen (NL) Universities. Based on MT analysis, a reinterpretation of the restitution mechanisms following spindle abnormalities was performed in this study. The fusion of the nuclei at prophase II occurs through the perinuclear MTs in the genotype with ‘fused spindles’. In genotypes with misoriented spindles, the ‘non-spindle’ cytoskeletal arrays,occurring at telophase II, are clue in determining the meiotic products such as dyads and triads. A particular MT array could be crucially involved in meiotic nuclear restitutions both at telophase I and II: the interzonal MTs. It is discussed which is the relationship between this array and the spindle orientation at meta-anaphase II. It is hypothesized that the fusion of non-sister nuclei at each pole depends on the lack of secondary interzonal MTs and on the short distance between nuclei. In the genotype with premature cytokinesis, effectively, a premature phragmoplast occurs at the end of meiosis I. Furthermore, two genotypes are desynaptic with a high degree of male fertility restored by the nuclear restitutions. However, no clear relationship was found between univalents and restitution mechanisms.

Identification, introgression, and validation of fruit volatile QTLs from a red-fruited wild tomato species.

Highlight Over 100 fruit volatile QTLs were identified in a RIL population derived from the red-fruited wild species Solanum pimpinellifolium and a fresh market tomato variety ‘Moneymaker’ and subsequently confirmed in introgression lines.

Meiotic nuclear restitution mechanisms in a triploid lily

Abstract Chromosome number and pollen stainability were evaluated in Lilium L. species (L. formosanum, L. miryophillum, L. regale), and in cultivars coming from Asiatic (Elite, Pollyanna, Vivaldi) and Oriental hybrid group (Cascade, Casablanca, Galilei). All the genotypes are diploid (2n=2x=24) except cv. Elite which results triploid (2n=3x=36). The pollen stainability ranged from 90 to 98% among diploids and from 80 to 90% in the triploid which exhibited pollen grains of different size, as well. A detailed analysis of microsporogenesis was carried out in the triploid cultivar. The chromosome associations at diakinesis were either trivalents or bivalents and univalents. Anaphases I and II exhibited lagging chromosomes and unequal distribution of chromosomes at the two poles. Single and double bridges plus acentric fragments formed possibly due to a paracentric inversion. Meiotic nuclear restitution mechanisms occurred following the failure of the reductional wall or, alternatively, of the equational wall. The analysis of sporads evidenced tetrads as well as dyads, triads and rare monads and poliads.

Whole-genome re-sequencing of two Italian tomato landraces reveals sequence variations in genes associated with stress tolerance, fruit quality and long shelf-life traits

Abstract Tomato is a high value crop and the primary model for fleshy fruit development and ripening. Breeding priorities include increased fruit quality, shelf life and tolerance to stresses. To contribute towards this goal, we re-sequenced the genomes of Corbarino (COR) and Lucariello (LUC) landraces, which both possess the traits of plant adaptation to water deficit, prolonged fruit shelf-life and good fruit quality. Through the newly developed pipeline Reconstructor, we generated the genome sequences of COR and LUC using datasets of 65.8 M and 56.4 M of 30–150 bp paired-end reads, respectively. New contigs including reads that could not be mapped to the tomato reference genome were assembled, and a total of 43, 054 and 44, 579 gene loci were annotated in COR and LUC. Both genomes showed novel regions with similarity to Solanum pimpinellifolium and Solanum pennellii. In addition to small deletions and insertions, 2, 000 and 1, 700 single nucleotide polymorphisms (SNPs) could exert potentially disruptive effects on 1, 371 and 1, 201 genes in COR and LUC, respectively. A detailed survey of the SNPs occurring in fruit quality, shelf life and stress tolerance related-genes identified several candidates of potential relevance. Variations in ethylene response components may concur in determining peculiar phenotypes of COR and LUC.

Molecular Mapping of Quantitative Trait Loci in Tomato

A major objective in modern biology is deciphering the genetic and molecular bases of natural phenotypic variation. Over the past three decades, the tomato clade (Solanum sect. Lycopersicon) has been a model system not only for the identification and positional cloning of quantitative trait loci (QTL), but also for the development of new molecular breeding strategies aimed at a more efficient exploration and exploitation of the rich biodiversity stored in wild germplasm for hundreds of biologically and agronomically relevant quantitative traits. The numerous QTL mapping studies conducted so far have resulted in the detection of several thousands of QTL. Despite this wealth of genetic information, the molecular bases have been revealed for only a handful of major QTL. The release of the tomato genome sequences, along with the rapid development of cost-effective next-generation sequencing (NGS) technologies, new mapping resources, and the evergrowing ‘‘omic’’ platforms, are holding the promise to reverse this trend. This deluge of genomic resources are undoubtedly reshaping QTL analyses also in this crop, allowing a reexamination of the variation and inheritance of complex traits at the intraspecific level, increasing the spectrum of potentially valuable alleles available for breeding. In this framework, precision phenotyping, advanced bioinformatics tools, as well as public phenotype “warehousing” databases are foreseen as the necessary tools to boost our understanding of the genetic and molecular architecture of quantitative traits, and to guarantee sustainable crop improvements in the face of an evergrowing human population and changing climates.

2n gametes inSolanum tuberosum dihaploids

Pollen stainability over two years and microsporogenesis were investigated in seven dihaploids extracted fromSolanum tuberosum tetraploids (AVRDC-1287.19, Conchita, Merrimack and W231). Two dihaploids proved to be male-sterile and male gamete abortion is likely to be post-meiotic because a regular meiosis occurred. The other dihaploids proved to be partially male-fertile and 2n pollen producers, as well. Almost all clones showed predominantly the formation of parallel spindles. Correlations estimated between the observed abnormalities in spindle orientation and the meiotic products evidenced a high correlation between parallel/fused spindles and dyads. The dihaploids were also used as parents in crosses with tetraploids. One berry with 44 seeds was obtained from dihaploid AVI 24 used as pollen parent in 4x × 2x crosses. After 2x × 4x crosses, three dihaploids including the two male-sterile were found to be 2n egg producers.The formation of 2n gametes inS. tuberosum dihaploids is discussed in relation to a direct use of dihaploids in sexual polyploidization schemes to combine useful traits in a superior genotype at 4x level.