A High Resolution Genetic Map Anchoring Scaffolds of the Sequenced Watermelon Genome

As part of our ongoing efforts to sequence and map the watermelon (Citrullus spp.) genome, we have constructed a high density genetic linkage map. The map positioned 234 watermelon genome sequence scaffolds (an average size of 1.41 Mb) that cover about 330 Mb and account for 93.5% of the 353 Mb of the assembled genomic sequences of the elite Chinese watermelon line 97103 (Citrullus lanatus var. lanatus). The genetic map was constructed using an F8 population of 103 recombinant inbred lines (RILs). The RILs are derived from a cross between the line 97103 and the United States Plant Introduction (PI) 296341-FR (C. lanatus var. citroides) that contains resistance to fusarium wilt (races 0, 1, and 2). The genetic map consists of eleven linkage groups that include 698 simple sequence repeat (SSR), 219 insertion-deletion (InDel) and 36 structure variation (SV) markers and spans ∼800 cM with a mean marker interval of 0.8 cM. Using fluorescent in situ hybridization (FISH) with 11 BACs that produced chromosome-specifc signals, we have depicted watermelon chromosomes that correspond to the eleven linkage groups constructed in this study. The high resolution genetic map developed here should be a useful platform for the assembly of the watermelon genome, for the development of sequence-based markers used in breeding programs, and for the identification of genes associated with important agricultural traits

The Sphagnome Project: enabling ecological and evolutionary insights through a genus-level sequencing project

Considerable progress has been made in ecological and evolutionary genetics with studies demonstrating how genes underlying plant and microbial traits can influence adaptation and even 'extend' to influence community structure and ecosystem level processes. Progress in this area is limited to model systems with deep genetic and genomic resources that often have negligible ecological impact or interest. Thus, important linkages between genetic adaptations and their consequences at organismal and ecological scales are often lacking. Here we introduce the Sphagnome Project, which incorporates genomics into a long-running history of Sphagnum research that has documented unparalleled contributions to peatland ecology, carbon sequestration, biogeochemistry, microbiome research, niche construction, and ecosystem engineering. The Sphagnome Project encompasses a genus-level sequencing effort that represents a new type of model system driven not only by genetic tractability, but by ecologically relevant questions and hypotheses

A high-density genetic map of the Medicago truncatula major freezing tolerance QTL on chromosome 6 reveals colinearity with a QTL related to freezing damage on Pisum sativum linkage group VI

Freezing is one of the most serious abiotic stress factors that affect cool-season legumes. It limits species geographic distribution and causes severe yield losses. Improving tolerance to freezing has long been a main concern for legume breeders. Medicago truncatula Gaertn. has been selected as a model species for legume biology. Various studies have shown significant macrosynteny between M. truncatula and agronomically important crop legumes. A major freezing tolerance quantitative trait locus (QTL), herein referred to as Mt-FTQTL6, was previously identified on M. truncatula chromosome 6. The physical location of this QTL was determined in this study and its corresponding chromosomal interval was enriched with additional markers. Markers were first developed using the draft sequence of M. truncatula euchromatin (release versions Mt3.0 and Mt3.5). Because Mt-FTQTL6 was found to coincide with an assembly gap, the Glycine max (L.) Merr. genome sequence was also used to generate markers. Five Mt-FTQTL6-linked markers were found to be common to a region on Pisum sativum L. linkage group VI harboring a QTL for freezing damage. A subset of markers was tested for transferability across 11 additional legume species. This study lays the groundwork for identifying the molecular basis of Mt-FTQTL6. Cross-legume markers will be useful in future efforts aiming to investigate the conservation of Mt-FTQTL6 in cool-season legumes and subsequently the existence of common mechanisms for response to freezing between M. truncatula and crop legumes

Effects of crystallographic orientation on corrosion behavior of magnesium single crystals

The corrosion behavior of magnesium single crystals with various crystallographic orientations was examined in this study. To identify the effects of surface orientation on the corrosion behavior in a systematic manner, single-crystal specimens with ten different rotation angles of the plane normal from the [0001] direction to the [1010] direction at intervals of 10&deg; were prepared and subjected to potentiodynamic polarization and potentiostatic tests as well as electrochemical impedance spectroscopy (EIS) measurements in 3.5 wt.% NaCl solution. Potentiodynamic polarization results showed that the pitting potential (E pit) first decreased from &minus;1.57 V SCE to &minus;1.64 V SCE with an increase in the rotation angle from 0&deg; to 40&deg;, and then increased to &minus;1.60 V SCE with a further increase in the rotation angle to 90&deg;. The results obtained from potentiostatic tests are also in agreement with the trend in potentiodynamic polarization tests as a function of rotation angle. A similar trend was also observed for the depressed semicircle and the total resistances in the EIS measurements due to the facile formation of MgO and Mg(OH)2 passive films on the magnesium surface. In addition, the amount of chloride in the passive film was found first to increase with an increase in rotation angle from 0&deg; to 40&deg;, then decrease with a further increase in rotation angle, indicating that the tendency to form a more protective passive film increased for rotation angle near 0&deg; [the (0001) plane] or 90&deg; [the (1010) plane]. <br /