Genome-Wide Association Studies Reveal Candidate Genes Related to Stem Diameter in Cucumber (Cucumis sativus L.)

Updated Gene Prediction of the Cucumber (9930) Genome through Manual Annotation

Thorough and precise gene structure annotations are essential for maximizing the benefits of genomic data and unveiling valuable genetic insights. The cucumber genome was first released in 2009 and updated in 2019. To increase the accuracy of the predicted gene models, 64 published RNA-seq data and 9 new strand-specific RNA-seq data from multiple tissues were used for manual comparison with the gene models. The updated annotation file (V3.1) contains an increased number (24,145) of predicted genes compared to the previous version (24,317 genes), with a higher BUSCO value of 96.9%. A total of 6231 and 1490 transcripts were adjusted and newly added, respectively, accounting for 31.99% of the overall gene tally. These newly added and adjusted genes were renamed (CsaV3.1_XGXXXXX), while genes remaining unaltered preserved their original designations. A random selection of 21 modified/added genes were validated using RT-PCR analyses. Additionally, tissue-specific patterns of gene expression were examined using the newly obtained transcriptome data with the revised gene prediction model. This improved annotation of the cucumber genome will provide essential and accurate resources for studies in cucumber.

A Genome-Wide Association Study Reveals the Genetic Mechanisms of Nutrient Accumulation in Spinach

Spinach is a significant source of vitamins, minerals, and antioxidants. These nutrients make it delicious and beneficial for human health. However, the genetic mechanism underlying the accumulation of nutrients in spinach remains unclear. In this study, we analyzed the content of chlorophyll a, chlorophyll b, oxalate, nitrate, crude fiber, soluble sugars, manganese, copper, and iron in 62 different spinach accessions. Additionally, 3,356,182 high-quality, single-nucleotide polymorphisms were found using resequencing and used in a genome-wide association study. A total of 2077 loci were discovered that significantly correlated with the concentrations of the nutritional elements. Data mining identified key genes in these intervals for four traits: chlorophyll, oxalate, soluble sugar, and Fe. Our study provides insights into the genetic architecture of nutrient variation and facilitates spinach breeding for good nutrition.

Genome-wide association study of drought tolerance traits in sugar beet germplasms at the seedling stage

Introduction: Sugar beets are an important crop for global sugar production. Intense drought and the increasing lack of water resources pose a great threat to sugar beet cultivation. It is a priority to investigate favourable germplasms and functional genes to improve the breeding of drought tolerant plants. Methods: Thus, in this study, 328 sugar beet germplasms were used in a genome-wide association study (GWAS) to identify single nucleotide polymorphism (SNP) markers and candidate genes associated with drought tolerance. Results: The results showed that under drought stress (9% PEG-6000), there were 11 significantly associated loci on chromosomes 2, 3, 5, 7, and 9 from the 108946 SNPs filtered using a mixed linear model (MLM). Genome-wide association analysis combined with qRT-PCR identified 13 genes that were significantly differentially expressed in drought-tolerant extreme materials. Discussion: These candidate genes mainly exhibited functions such as regulating sugar metabolism, maintaining internal environmental stability and participating in photosystem repair. This study provides valuable information for exploring the molecular mechanisms of drought tolerance and improvement in sugar beet.

QTL mapping reveals candidate genes for main agronomic traits in Luffa based on a high-resolution genetic map

Luffa is an important medicinal and edible vegetable crop of Cucurbitaceae. Strong heterosis effects and strikingly complementary characteristics were found between the two domesticated Luffa cultivars, Luffa acutangula and Luffa cylindrica. To explore the genetic basis underlying their important agronomic traits, we constructed the first interspecific high-density genetic linkage map using a BC₁ population of 110 lines derived from a cross between S1174 (Luffa acutangula) and P93075 (Luffa cylindrica). The map spanned a total of 2246.74 cM with an average distance of 0.48 cM between adjacent markers. Thereafter, a large-scale field-based quantitative trait loci (QTLs) mapping was conducted for 25 important agronomic traits and 40 significant genetic loci distributed across 11 chromosomes were detected. Notably, a vital QTL (qID2) located on chromosome 9 with a minimum distance of 23 kb was identified to be responsible for the internode diameter and explained 11% of the phenotypic variation. Lac09g006860 (LacCRWN3), encoding a nuclear lamina protein involved in the control of nuclear morphology, was the only gene harbored in qID2. Sequence alignment showed completely different promoter sequences between the two parental alleles of LacCRWN3 except for some nonsynonymous single nucleotide polymorphisms (SNPs) in exons, and the expression level in thick-stem P93075 was distinctively higher than that in thin-stem S1174. According to the natural variation analysis of a population of 183 inbred lines, two main haplotypes were found for LacCRWN3: the P93075-like and S1174-like, with the former haplotype lines exhibiting significantly thicker internode diameters than those of the latter haplotype lines. It showed that LacCRWN3, as the only CRWN3 gene in Cucurbitaceae, was the most likely candidate gene regulating the internode diameter of Luffa. Our findings will be beneficial for deciphering the molecular mechanism of key phenotypic traits and promoting maker-assisted breeding in Luffa.