Correction: Structural variation underlies functional diversity at methyl salicylate loci in tomato.

[This corrects the article DOI: 10.1371/journal.pgen.1010751.].

Redesigning the tomato fruit shape for mechanized production.

Crop breeding for mechanized harvesting has driven modern agriculture. In tomato, machine harvesting for industrial processing varieties became the norm in the 1970s. However, fresh-market varieties whose fruits are suitable for mechanical harvesting are difficult to breed because of associated reduction in flavour and nutritional qualities. Here we report the cloning and functional characterization of fs8.1, which controls the elongated fruit shape and crush resistance of machine-harvestable processing tomatoes. FS8.1 encodes a non-canonical GT-2 factor that activates the expression of cell-cycle inhibitor genes through the formation of a transcriptional module with the canonical GT-2 factor SlGT-16. The fs8.1 mutation results in a lower inhibitory effect on the cell proliferation of the ovary wall, leading to elongated fruits with enhanced compression resistance. Our study provides a potential route for introducing the beneficial allele into fresh-market tomatoes without reducing quality, thereby facilitating mechanical harvesting.

Structural variation underlies functional diversity at methyl salicylate loci in tomato.

Methyl salicylate is an important inter- and intra-plant signaling molecule, but is deemed undesirable by humans when it accumulates to high levels in ripe fruits. Balancing the tradeoff between consumer satisfaction and overall plant health is challenging as the mechanisms regulating volatile levels have not yet been fully elucidated. In this study, we investigated the accumulation of methyl salicylate in ripe fruits of tomatoes that belong to the red-fruited clade. We determine the genetic diversity and the interaction of four known loci controlling methyl salicylate levels in ripe fruits. In addition to Non-Smoky Glucosyl Transferase 1 (NSGT1), we uncovered extensive genome structural variation (SV) at the Methylesterase (MES) locus. This locus contains four tandemly duplicated Methylesterase genes and genome sequence investigations at the locus identified nine distinct haplotypes. Based on gene expression and results from biparental crosses, functional and non-functional haplotypes for MES were identified. The combination of the non-functional MES haplotype 2 and the non-functional NSGT1 haplotype IV or V in a GWAS panel showed high methyl salicylate levels in ripe fruits, particularly in accessions from Ecuador, demonstrating a strong interaction between these two loci and suggesting an ecological advantage. The genetic variation at the other two known loci, Salicylic Acid Methyl Transferase 1 (SAMT1) and tomato UDP Glycosyl Transferase 5 (SlUGT5), did not explain volatile variation in the red-fruited tomato germplasm, suggesting a minor role in methyl salicylate production in red-fruited tomato. Lastly, we found that most heirloom and modern tomato accessions carried a functional MES and a non-functional NSGT1 haplotype, ensuring acceptable levels of methyl salicylate in fruits. Yet, future selection of the functional NSGT1 allele could potentially improve flavor in the modern germplasm.

Blossom-end rot: a century-old problem in tomato (Solanum lycopersicum L.) and other vegetables.

Blossom-end rot (BER) is a devastating physiological disorder affecting vegetable production worldwide. Extensive research into the physiological aspects of the disorder has demonstrated that the underlying causes of BER are associated with perturbed calcium (Ca2+) homeostasis and irregular watering conditions in predominantly cultivated accessions. Further, Reactive Oxygen Species (ROS) are critical players in BER development which, combined with unbalanced Ca2+ concentrations, greatly affect the severity of the disorder. The availability of a high-quality reference tomato genome as well as the whole genome resequencing of many accessions has recently permitted the genetic dissection of BER in segregating populations derived from crosses between cultivated tomato accessions. This has led to the identification of five loci contributing to BER from several studies. The eventual cloning of the genes contributing to BER would result in a deeper understanding of the molecular bases of the disorder. This will undoubtedly create crop improvement strategies for tomato as well as many other vegetables that suffer from BER.

Identification of blossom-end rot loci using joint QTL-seq and linkage-based QTL mapping in tomato.

KEY MESSAGE: Blossom-End Rot is Quantitatively Inherited and Maps to Four Loci in Tomato. Blossom-end rot (BER) is a devastating physiological disorder that affects tomato and other vegetables, resulting in significant crop losses. To date, most studies on BER have focused on the environmental factors that affect calcium translocation to the fruit; however, the genetic basis of this disorder remains unknown. To investigate the genetic basis of BER, two F2 and F3:4 populations along with a BC1 population that segregated for BER occurrence were evaluated in the greenhouse. Using the QTL-seq approach, quantitative trait loci (QTL) associated with BER Incidence were identified at the bottom of chromosome (ch) 3 and ch11. Additionally, linkage-based QTL mapping detected another QTL, BER3.1, on ch3 and BER4.1 on ch4. To fine map the QTLs identified by QTL-seq, recombinant screening was performed. BER3.2, the major BER QTL on ch3, was narrowed down from 5.68 to 1.58 Mbp with a 1.5-LOD support interval (SI) corresponding to 209 candidate genes. BER3.2 colocalizes with the fruit weight gene FW3.2/SlKLUH, an ortholog of cytochrome P450 KLUH in Arabidopsis. Further, BER11.1, the major BER QTL on ch11, was narrowed down from 3.99 to 1.13 Mbp with a 1.5-LOD SI interval comprising of 141 candidate genes. Taken together, our results identified and fine mapped the first loci for BER resistance in tomato that will facilitate marker-assistant breeding not only in tomato but also in many other vegetables suffering for BER.

The effects of UV radiation during the vegetative period on antioxidant compounds and postharvest quality of broccoli (Brassica oleracea L.).

In this study, the effects of supplementary UV radiation during the vegetative period on antioxidant compounds, antioxidant activity and postharvest quality of broccoli heads during long term storage was studied. The broccolis were grown under three different doses of supplementary UV radiation (2.2, 8.8 and 16.4 kJ/m(2)/day) in a soilless system in a glasshouse. Harvested broccoli heads were stored at 0 °C in modified atmosphere packaging for 60 days. The supplementary UV radiation (280-315 nm) during the vegetative period significantly decreased total carotenoid, the chlorophyll a and chlorophyll b content but increased the ascorbic acid, total phenolic and flavonoid contents of broccolis. All supplementary UV treatments slightly reduced the antioxidant activity of the broccolis, however, no remarkable change was observed between 2.2 and 8.8 kJ/m(2) radiation levels. The sinigrin and glucotropaeolin contents of the broccolis were substantially increased by UV treatments. The prolonged storage period resulted in decreased ascorbic acid, total phenolic and flavonoid contents, as well as antioxidant activity. Discoloration of the heads, due to decreased chlorophyll and carotenoid contents, was also observed with prolonged storage duration. Glucosinolates levels showed an increasing tendency till the 45th day of storage, and then their levels started to decline. The weight loss of broccoli heads during storage progressively increased with storage time in all treatments. Total soluble solids, solids content and titratable acidity decreased continuously during storage. Titratable acidity was not affected by UV radiation doses during the storage time whereas soluble solids and solids content (dry matter) were significantly affected by UV doses. Supplementary UV radiation increased the lightness (L*) and chroma (C*) values of the broccoli heads. Pre-harvest UV radiation during vegetative period seems to be a promising tool for increasing the beneficial health components of broccolis.