bims-plasge 2019-10-27 papers

Front Plant Sci. 2019 ;10 1240

Fine Mapping of Lycopene Content and Flesh Color Related Gene and Development of Molecular Marker-Assisted Selection for Flesh Color in Watermelon (Citrullus lanatus).

Chaonan Wang, Aohan Qiao, Xufeng Fang, Lei Sun, Peng Gao, Angela R Davis, Shi Liu, Feishi Luan.

Lycopene content and flesh color are important traits determined by a network of carotenoid metabolic pathways in watermelon. Based on our previous study of genetic inheritance and initial mapping using F2 populations of LSW-177 (red flesh) × cream of Saskatchewan (pale yellow flesh), red flesh color was controlled by one recessive gene regulating red and pale yellow pigmentation, and a candidate region related to lycopene content was detected spanning a 392,077-bp region on chromosome 4. To obtain a more precise result for further study, three genetic populations and a natural panel of 81 watermelon accessions with different flesh colors were used in this research. Herein, we narrowed the preliminary mapping region to 41,233 bp with the linkage map generated from F2 populations of LSW-177 (red flesh) × cream of Saskatchewan (pale yellow flesh) with 1,202 individuals. Two candidate genes, Cla005011 and Cla005012, were found in the fine mapping region; therein Cla005011 was a key locus annotated as a lycopene β-cyclase gene. Phylogenetic tree analysis showed that Cla005011 was the closest relative gene in gourd. LSW-177 × PI 186490 (white flesh) and another BC1 population derived from garden female (red flesh) × PI 186490 were generated to verify the accuracy of the red flesh candidate gene region. By analyzing the expression levels of candidate genes in different developmental stages of different color watermelon varieties, Cla005011 for the expression differences was not the main reason for the flesh color variation between COS and LSW-177. This indicated that the LCYB gene might regulate fruit color changes at the protein level. A new marker-assisted selection system to identify red and yellow flesh colors in watermelon was developed with flesh color-specific CAPS markers and tested in 81 watermelon accessions.

Keywords: CAPS markers; flesh color; gene mapping; lycopene; marker-assisted selection (MAS)

DOI: https://doi.org/10.3389/fpls.2019.01240

Theor Appl Genet. 2019 Oct 22.

Transposition of a non-autonomous DNA transposon in the gene coding for a bHLH transcription factor results in a white bulb color of onions (Allium cepa L.).

Changyeong Jo, Sunggil Kim.

KEY MESSAGE: A DNA transposon was found in the gene encoding a bHLH transcription factor. Genotypes of the marker tagging this DNA transposon perfectly co-segregated with color phenotypes in large F2:3 populations A combined approach of bulked segregant analysis and RNA-Seq was used to isolate causal gene for C locus controlling white bulb color in onions (Allium cepa L.). A total of 114 contigs containing homozygous single nucleotide polymorphisms (SNPs) between white and yellow bulked RNAs were identified. Four of them showed high homologies with loci clustered in the middle of chromosome 5. SNPs in 34 contigs were confirmed by sequencing of PCR products. One of these contigs showed perfect linkage to the C locus in F2:3 populations consisting of 2491 individuals. However, genotypes of molecular marker tagging this contig were inconsistent with color phenotypes of diverse breeding lines. A total of 146 contigs showed differential expression between yellow and white bulks. Among them, transcription levels of B2 gene encoding a bHLH transcription factor were significantly reduced in white RNA bulk and F2:3 individuals, although there was no SNP in the coding region. Phylogenetic analysis showed that onion B2 was orthologous to bHLH-coding genes regulating anthocyanin biosynthesis pathway in other plant species. Promoter regions of B2 gene were obtained by genome walking and a 577-bp non-autonomous DNA transposon designated as AcWHITE was found in the white allele. Molecular marker tagging AcWHITE showed perfect linkage with the C locus. Marker genotypes of the white allele were detected in some white accessions. However, none of tested red or yellow onions contained AcWHITE insertion, implying that B2 gene was likely to be a casual gene for the C locus.

Keywords: Molecular marker; Onion (Allium cepa L.); RNA-Seq; White bulb color; bHLH transcription factor

DOI: https://doi.org/10.1007/s00122-019-03460-8

Hortic Res. 2019 ;6 95

Copy numbers of mitochondrial genes change during melon leaf development and are lower than the numbers of mitochondria.

Jia Shen, Yuejian Zhang, Michael J Havey, Weisong Shou.

Melon is a useful plant species for studying mitochondrial genetics because it contains one of the largest and structurally diverse mitochondrial genomes among all plant species and undergoes paternal transmission of mitochondria. We used droplet digital (dd) PCR in combination with flow cytometric determination of nuclear DNA quantities to determine the absolute per-cell copy numbers of four mitochondrial genes (nad9, rps1, matR, and atp6) across four stages of melon leaf development. The copy numbers of these mitochondrial genes not only varied during leaf development but also differed among each other, and there was no correlation between the copy numbers of the mitochondrial genes and their transcript levels. The gene copy numbers varied from approximately 36.8 ± 4.5 (atp6 copies in the 15th leaf) to approximately 82.9 ± 5.7 (nad9 copies in the 9th leaf), while the mean number of mitochondria was approximately 416.6 ± 182.7 in the 15th leaf and 459.1 ± 228.2 in the 9th leaf. These observations indicate that the leaf cells of melon do not contain sufficient copies of mitochondrial genes to ensure that every mitochondrion possesses the entire mitochondrial genome. Given this cytological evidence, our results indicate that mtDNA in melon exists as a sub-genomic molecule rather than as a single-master circle and that the copy numbers of individual mitochondrial genes may vary greatly. An improved understanding of the molecular mechanism(s) controlling the relative prevalence and transmission of sub-genomic mtDNA molecules should provide insights into the continuity of the mitochondrial genome across generations.

Keywords: Plant cell biology; Plant genetics

DOI: https://doi.org/10.1038/s41438-019-0177-8