Intra- and inter-specific reproductive barriers in the tomato clade.

Tomato (Solanum lycopersicum L.) domestication and later introduction into Europe resulted in a genetic bottleneck that reduced genetic variation. Crosses with other wild tomato species from the Lycopersicon clade can be used to increase genetic diversity and improve important agronomic traits such as stress tolerance. However, many species in the Lycopersicon clade have intraspecific and interspecific incompatibility, such as gametophytic self-incompatibility and unilateral incompatibility. In this review, we provide an overview of the known incompatibility barriers in Lycopersicon. We begin by addressing the general mechanisms self-incompatibility, as well as more specific mechanisms in the Rosaceae, Papaveraceae, and Solanaceae. Incompatibility in the Lycopersicon clade is discussed, including loss of self-incompatibility, species exhibiting only self-incompatibility and species presenting both self-compatibility and self-incompatibility. We summarize unilateral incompatibility in general and specifically in Lycopersicon, with details on the 'self-compatible x self-incompatible' rule, implications of self-incompatibility in unilateral incompatibility and self-incompatibility-independent pathways of unilateral incompatibility. Finally, we discuss advances in the understanding of compatibility barriers and their implications for tomato breeding.

The Halophyte Species Solanum chilense Dun. Maintains Its Reproduction despite Sodium Accumulation in Its Floral Organs.

Salinity is a growing global concern that affects the yield of crop species, including tomato (Solanum lycopersicum). Its wild relative Solanum chilense was reported to have halophyte properties. We compared salt resistance of both species during the reproductive phase, with a special focus on sodium localization in the flowers. Plants were exposed to NaCl from the seedling stage. Salinity decreased the number of inflorescences in both species but the number of flowers per inflorescence and sepal length only in S. lycopersicum. External salt supply decreased the stamen length in S. chilense, and it was associated with a decrease in pollen production and an increase in pollen viability. Although the fruit set was not affected by salinity, fruit weight and size decreased in S. lycopersicum. Concentrations and localization of Na, K, Mg, and Ca differed in reproductive structures of both species. Inflorescences and fruits of S. chilense accumulated more Na than S. lycopersicum. Sodium was mainly located in male floral organs of S. chilense but in non-reproductive floral organs in S. lycopersicum. The expression of Na transporter genes differed in flowers of both species. Overall, our results indicated that S. chilense was more salt-resistant than S. lycopersicum during the reproductive phase and that differences could be partly related to dissimilarities in element distribution and transport in flowers.

Comparison of Drought and Heat Resistance Strategies among Six Populations of Solanum chilense and Two Cultivars of Solanum lycopersicum.

Within the tomato clade, Solanum chilense is considered one of the most promising sources of genes for tomato (S. lycopersicum) selection to biotic and abiotic stresses. In this study, we compared the effects of drought, high temperature, and their combination in two cultivars of S. lycopersicum and six populations of S. chilense, differing in their local habitat. Plants were grown at 21/19 °C or 28/26 °C under well-watered and water-stressed conditions. Plant growth, physiological responses, and expression of stress-responsive genes were investigated. Our results demonstrated strong variability among accessions. Differences in plant growth parameters were even higher among S. chilense populations than between species. The effects of water stress, high temperature, and their combination also differed according to the accession, suggesting differences in stress resistance between species and populations. Overall, water stress affected plants more negatively than temperature from a morpho-physiological point of view, while the expression of stress-responsive genes was more affected by temperature than by water stress. Accessions clustered in two groups regarding resistance to water stress and high temperature. The sensitive group included the S. lycopersicum cultivars and the S. chilense populations LA2931 and LA1930, and the resistant group included the S. chilense populations LA1958, LA2880, LA2765, and LA4107. Our results suggested that resistance traits were not particularly related to the environmental conditions in the natural habitat of the populations. The expression of stress-responsive genes was more stable in resistant accessions than in sensitive ones in response to water stress and high temperature. Altogether, our results suggest that water stress and high temperature resistance in S. chilense did not depend on single traits but on a combination of morphological, physiological, and genetic traits.

Tomato Fruit Development and Metabolism.

Tomato (Solanum lycopersicum L.) belongs to the Solanaceae family and is the second most important fruit or vegetable crop next to potato (Solanum tuberosum L.). It is cultivated for fresh fruit and processed products. Tomatoes contain many health-promoting compounds including vitamins, carotenoids, and phenolic compounds. In addition to its economic and nutritional importance, tomatoes have become the model for the study of fleshy fruit development. Tomato is a climacteric fruit and dramatic metabolic changes occur during its fruit development. In this review, we provide an overview of our current understanding of tomato fruit metabolism. We begin by detailing the genetic and hormonal control of fruit development and ripening, after which we document the primary metabolism of tomato fruits, with a special focus on sugar, organic acid, and amino acid metabolism. Links between primary and secondary metabolic pathways are further highlighted by the importance of pigments, flavonoids, and volatiles for tomato fruit quality. Finally, as tomato plants are sensitive to several abiotic stresses, we briefly summarize the effects of adverse environmental conditions on tomato fruit metabolism and quality.

Comparative in vitro/in situ approaches to three biomarker responses of Myriophyllum alterniflorum exposed to metal stress.

Surface water pollution by trace metal elements constitutes problems for both public and terrestrial/aquatic ecosystem health. Myriophyllum alterniflorum (alternate watermilfoil), an aquatic macrophyte known for bioaccumulating this type of pollutant, is an attractive species for plant biomonitoring within the scope of environmental research. The two metal elements copper (Cu) and cadmium (Cd) are considered in the present study. Cu is essential for plant development at low concentrations, while very high Cu concentrations are detrimental or even lethal to most plants. On the other hand, Cd is usually toxic even at low concentrations since it adversely affects the physiological plant functions. In order to check whether watermilfoil could be used for the in situ biomonitoring of Cu or Cd pollution in rivers, the plant biomarker sensitivity is first tested during long-term in vitro assays. Three markers specific to oxidative stress (glucose-6-phosphate dehydrogenase, malondialdehyde and α-tocopherol) are evaluated by varying the pollutant concentration levels. Given the absence of effective correlations between Cu and all biomarkers, the response profiles actually reveal a dependency between Cd concentration and malondialdehyde or α-tocopherol biomarkers. Conversely, preliminary in situ assays performed at 14 different localities demonstrate some clear correlations between all biomarkers and Cu, whereas the scarcity of Cd-contaminated rivers prevents using the statistical data. Consequently, the three indicated biomarkers appear to be effective for purposes of metal exposure analyses; moreover, the in situ approach, although preliminary, proves to be paramount in developing water biomonitoring bases.

Pivotal roles of environmental sensing and signaling mechanisms in plant responses to climate change.

Climate change reshapes the physiology and development of organisms through phenotypic plasticity, epigenetic modifications, and genetic adaptation. Under evolutionary pressures of the sessile lifestyle, plants possess efficient systems of phenotypic plasticity and acclimation to environmental conditions. Molecular analysis, especially through omics approaches, of these primary lines of environmental adjustment in the context of climate change has revealed the underlying biochemical and physiological mechanisms, thus characterizing the links between phenotypic plasticity and climate change responses. The efficiency of adaptive plasticity under climate change indeed depends on the realization of such biochemical and physiological mechanisms, but the importance of sensing and signaling mechanisms that can integrate perception of environmental cues and transduction into physiological responses is often overlooked. Recent progress opens the possibility of considering plant phenotypic plasticity and responses to climate change through the perspective of environmental sensing and signaling. This review aims to analyze present knowledge on plant sensing and signaling mechanisms and discuss how their structural and functional characteristics lead to resilience or hypersensitivity under conditions of climate change. Plant cells are endowed with arrays of environmental and stress sensors and with internal signals that act as molecular integrators of the multiple constraints of climate change, thus giving rise to potential mechanisms of climate change sensing. Moreover, mechanisms of stress-related information propagation lead to stress memory and acquired stress tolerance that could withstand different scenarios of modifications of stress frequency and intensity. However, optimal functioning of existing sensors, optimal integration of additive constraints and signals, or memory processes can be hampered by conflicting interferences between novel combinations and novel changes in intensity and duration of climate change-related factors. Analysis of these contrasted situations emphasizes the need for future research on the diversity and robustness of plant signaling mechanisms under climate change conditions.