Lokus SSR Berasosiasi Karakter Tahan Penyakit Mati-Pohon Durian Berdasarkan Bulked Pseudo-Segregant Analysis (SSR Loci Associated to Resistance Traits to Durian Die-Back based on Bulked Pseudo-Segregant Analysis)

<p>Penyakit mati-pohon disebabkan cendawan Pythiaceae khususnya Phytophtora palmivora, Pythium vexans, dan Pythium cucurbitacearum menjadi salah satu kendala utama dalam budidaya durian. Di antara upaya pengendaliannya adalah melalui pemuliaan dan seleksi tanaman tahan berbasis molekuler menggunakan marka SSR. Penelitian untuk mengidentifikasi lokus SSR yang berasosiasi dengan karakter tahan penyakit mati-pohon pada durian telah dilaksanakan di Laboratorium Genetika Tumbuhan SITH-ITB dari bulan April sampai dengan Desember 2014. Penelitian dilaksanakan secara bulked pseudo-segregant analysis dua pool DNA durian tahan dan rentan. Amplifikasi lokus SSR menggunakan 77 pasang primer mikrosatelit berlabel fluorescent. Produk amplifikasi dibaca menggunakan GeneMarker v.2.4.0., setiap puncak pancaran fluorescent yang memiliki nilai intensitas tinggi dipilih sebagai alel. Pembandingan panjang alel dilakukan di antara dua pool dan pembanding aksesi tahan. Lokus yang memiliki alel berbeda antara dua pool tetapi memiliki alel sama dengan pembanding dianggap sebagai marka yang berasosiasi dengan sifat tahan durian terhadap Pythiaceae. Hasil analisis ditemukan tiga lokus mDz03F10, mDz4B2, dan mDz3B1 dengan motif berturut-turut (GAA)3.A(GA)4, (GAGT)2ttGAGT, dan (TTTTATG)2(GCCC)2 teridentifikasi sebagai marka yang berasosiasi dengan karakter tahan Pythiaceae. Hasil analisis ini memerlukan satu langkah validasi untuk meyakinkan keterpautan marka dengan karakter target sebelum digunakan sebagai marka molekuler.</p><p><strong>Keywords</strong></p><p>Durian; SSR; BpSA; Tahan; <em>Pythiaceae</em></p><p><strong>Abstract</strong></p><p>Die-back disease caused by Pythiaceae especially Phytophtora palmivora, Pythium vexans, and Pythium cucurbitacearum is one of the obstacles in durian cultivation. An effort to control this disease is through breeding and selection of resistant plants based on molecular assays such as SSR markers. Research to identify SSR loci associated with durian die-back resistance was done at Plant Genetics Laboratory, SITH-ITB from April to December 2014. The research was conducted through bulked pseudo-segregant analysis of two DNA pools, resistance, and susceptible durians. Amplification of SSR loci was carried out by using 77 fluorescent labeled primers. Amplification products were analyzed using GeneMarker v.2.4.0. Fluorescent peak with high intensity was considered as a selected allele. Comparison of allele length was executed amongst two pools and resistance reference. A locus showed different allele between two pools, while it given the same allele to reference was considered as SSR marker associated with Phytiaceae resistance. The analysis were found three loci, mDz03F10, mDz4B2, and mDz3B1 with motif of (GAA)3.A(GA)4, (GAGT)2ttGAGT, and (TTTTATG)2(GCCC)2 recpectively identified as SSR markers associated to die-back resistance. This result, therefore, requires further validation to convince markers association to target traits before they are used as molecular markers.</p>

Identification of two QTLs associated with high fruit acidity in apple using pooled genome sequencing analysis

Acidity is a critical component determining apple fruit quality. Previous studies reported two major acidity quantitative trait loci (QTLs) on linkage groups (LGs) 16 (Ma) and 8 (Ma3), respectively, and their homozygous genotypes mama and ma3ma3 usually confer low titratable acidity (TA) (<3.0 mg ml−1) to apple fruit. However, apples of genotypes Ma- (MaMa and Mama) or Ma3- (Ma3Ma3 and Ma3ma3) frequently show an acidity range spanning both regular (TA 3.0–10.0 mg ml−1) and high (TA > 10 mg ml−1) acidity levels. To date, the genetic control for high-acidity apples remains essentially unknown. In order to map QTLs associated with high acidity, two genomic DNA pools, one for high acidity and the other for regular acidity, were created in an interspecific F1 population Royal Gala (Malus domestica) × PI 613988 (M. sieversii) of 191 fruit-bearing progenies. By Illumina paired-end sequencing of the high and regular acidity pools, 1,261,640 single-nucleotide variants (SNVs) commonly present in both pools were detected. Using allele frequency directional difference and density (AFDDD) mapping approach, one region on chromosome 4 and another on chromosome 6 were identified to be putatively associated with high acidity, and were named Ma6 and Ma4, respectively. Trait association analysis of DNA markers independently developed from the Ma6 and Ma4 regions confirmed the mapping of Ma6 and Ma4. In the background of MaMa, 20.6% of acidity variation could be explained by Ma6, 28.5% by Ma4, and 50.7% by the combination of both. The effects of Ma6 and Ma4 in the background of Mama were also significant, but lower. These findings provide important genetic insight into high acidity in apple.

Genome-wide SNP genotyping of DNA pools identifies untapped landraces and genomic regions that could enrich the maize breeding pool

ABSTRACTMaize landraces preserved in genebanks have a large genetic diversity that is still poorly characterized and underexploited in modern breeding programs. Here, we genotyped DNA pools from 156 American and European landraces with a 50K SNP Illumina array to study the effect of both human selection and environmental adaptation on the genome-wide diversity of maize landraces. Genomic diversity of landraces varied strongly in different parts of the genome and with geographic origin. We detected selective footprints between landraces of different geographic origin in genes involved in the starch pathway (Su1, Waxy1), flowering time (Zcn8, Vgt3, ZmCCT9) and tolerance to abiotic and biotic stress (ZmASR, NAC and dkg genes). Landrace diversity was compared to that of (i) 327 inbred lines representing American and European diversity (“CK lines) and (ii) 103 new lines derived directly from landraces (“DH-SSD lines”). We observed limited diversity loss or selective sweep between landraces and CK lines, except in peri-centromeric regions. However, analysis of modified Roger’s distance between landraces and the CK lines showed that most landraces were not closely related to CK lines. Assignment of CK lines to landraces using supervised analysis showed that only a few landraces, such as Reid’s Yellow Dent, Lancaster Surecrop and Lacaune, strongly contributed to modern European and American breeding pools. Haplotype diversity of CK lines was more enriched by DH-SSD lines that derived from the landraces with no related lines and the lowest contribution to CK lines. Our approach opens an avenue for the identification of promising landraces for pre-breeding.SIGNIFICANCE STATEMENTSMaize landraces are a valuable source of genetic diversity for addressing the challenges of climate change and the requirements of low input agriculture as they have been long selected to be well adapted to local agro-climatic conditions and human uses. However, they are underutilized in modern breeding programs because they are poorly characterized, genetically heterogeneous and exhibit poor agronomic performance compared to elite hybrid material. In this study, we developed a high-throughput approach to identify landraces that could potentially enlarge the genetic diversity of modern breeding pools. We genotyped DNA pools from landraces using 50K array technology, which is widely used by breeders to characterize the genetic diversity of inbred lines. To identify landraces that could enrich the modern maize germplasm, we estimated their contribution to inbred lines using supervised analysis and a new measurement of genetic distance.

Culicidae-centric metabarcoding through targeted use of D2 ribosomal DNA primers

A practical limitation to many metabarcoding initiatives is that sampling methods tend to collect many non-target taxa, which become “amplicon noise” that can saturate Next Generation Sequencing results and lead to both financial and resource inefficiencies. An available molecular tool that can significantly decrease these non-target amplicons and decrease the need for pre-DNA-extraction sorting of bycatch is the design of PCR primers tailored to the taxa under investigation. We assessed whether the D2 extension segment of the 28S ribosomal operon can limit this shortcoming within the context of mosquito (Culicidae) monitoring. We designed PCR primers that are fully conserved across mosquitos and exclude from amplification most other taxa likely to be collected with current sampling apparatuses. We show that, given enough sequencing depth, D2 is an effective marker for the detection of mosquito sequences within mock genomic DNA pools. As few as 3,050 quality-filtered Illumina reads were able to recover all 17 species in a bulk pool containing as little as 0.2% of constituent DNA from single taxa. We also mixed these mosquito DNA pools with high concentrations of non-Culicidae bycatch DNA and show that the component mosquito species are generally still recoverable and faithful to their original relative frequencies. Finally, we show that there is little loss of fidelity in abundance parameters when pools from degraded DNA samples were sequenced using the D2 primers.

The quest for absolute abundance: the use of internal standards for DNA-based microbial and community ecology

To characterize microbiomes and other ecological assemblages, ecologists routinely sequence and compare loci that differ among focal taxa. Counts of these sequences convey information regarding the occurrence and relative abundances of taxa, but provide no direct measure of their absolute abundances, due to the technical limitations of the sequencing process. The relative abundances in compositional data are inherently constrained and difficult to interpret. The incorporation of internal standards (ISDs; colloquially referred to as ``spike-ins'') into DNA pools can ameliorate the problems posed by relative abundance data and allow absolute abundances to be approximated. Unfortunately, many laboratory and sampling biases cause ISDs to underperform or fail. Here, we discuss how careful deployment of ISDs can avoid these complications and be an integral component of well-designed studies seeking to characterize ecological assemblages via sequencing of DNA.

Rapid Identification of a Genomic Region Conferring Dwarfism in Rapeseed (Brassica napus L.) YA2016-12

Plant height is a vital agronomic trait for crops, including oilseed crops such as rapeseed (Brassica napus L.). It affects the crop yield, oil content, and lodging resistance in rapeseed. In this study, we investigated a dwarf trait controlled by a semi-dominant allele in rapeseed. A dwarf line, YA2016-12, was crossed with a tall line, G184-189, and an F2 population was established. Forty of the tallest plants and 40 of the shortest plants from the F2 population were selected and two DNA pools (tall and dwarf) were constructed by the bulked segregant analysis (BSA) method. The two DNA pools and two parental DNAs were then re-sequenced. A sliding window analysis was used to calculate the Δ(SNP-index) and discover an association region on chromosome A03 with a length of 12.4 Mb. Within this region, we found 1225 genes, including 811 genes with non-synonymous or frameshift mutations between YA2016-12 and G184-189. Alignment to known plant height-related orthologs in Arabidopsis thaliana, as well as KEGG pathway and gene ontology annotations, was used to identify nine candidate genes (BnaA03g31770D, BnaA03g37960D, BnaA03g24740D, BnaA03g40550D, BnaA03g26120D, BnaA03g35130D, BnaA03g42350D, BnaA03g25610D, and BnaA03g39850D) involved in gibberellin or cytokinin signaling. Identification of the causal gene for this trait, and of genetic markers linked to favorable alleles, has potential utility for marker-assisted selection to breed rapeseed varieties with improved height.