Preparing long probes by an asymmetric polymerase chain reaction-based approach for multiplex ligation-dependent probe amplification

MLPA-Based Analysis of Copy Number Variation in Plant Populations

Copy number variants (CNVs) are intraspecies duplications/deletions of large DNA segments (>1 kb). A growing number of reports highlight the functional and evolutionary impact of CNV in plants, increasing the need for appropriate tools that enable locus-specific CNV genotyping on a population scale. Multiplex ligation-dependent probe amplification (MLPA) is considered a gold standard in genotyping CNV in humans. Consequently, numerous commercial MLPA assays for CNV-related human diseases have been created. We routinely genotype complex multiallelic CNVs in human and plant genomes using the modified MLPA procedure based on fully synthesized oligonucleotide probes (90-200 nt), which greatly simplifies the design process and allows for the development of custom assays. Here, we present a step-by-step protocol for gene-specific MLPA probe design, multiplexed assay setup and data analysis in a copy number genotyping experiment in plants. As a case study, we present the results of a custom assay designed to genotype the copy number status of 12 protein coding genes in a population of 80 Arabidopsis accessions. The genes were pre-selected based on whole genome sequencing data and are localized in the genomic regions that display different levels of population-scale variation (non-variable, biallelic, or multiallelic, as well as CNVs overlapping whole genes or their fragments). The presented approach is suitable for population-scale validation of the CNV regions inferred from whole genome sequencing data analysis and for focused analysis of selected genes of interest. It can also be very easily adopted for any plant species, following optimization of the template amount and design of the appropriate control probes, according to the general guidelines presented in this paper.

Sequencing data and MLPA analysis data in support of the effectiveness and reliability of an asymmetric PCR-Based approach in preparing long MLPA probes

ABI PRISM 3100 Genetic Analyzer, a multi-color fluorescence-based DNA analysis system with 16 capillaries operating in parallel, was ideal tool both for DNA sequencing and DNA fragment analysis [1,2]. To demonstrate the effectiveness and reliability of an asymmetric PCR-Based approach (X.Y. Ling, G.M. Zhang, G. Pan, H. Long, Y.H. Cheng, C.Y. Xiang, L. Kang, F. Chen, Z.N. Chen, Preparing long probes by an asymmetric PCR-based approach for multiplex ligation-dependent probe amplification (MLPA), Anal. Biochem. (2015), http://dx.doi.org/10.1016/j.ab.2015.03.031, in press) in preparing the long MLPA probes that were generated with a M13-based method before [4], some prepared long MLPA probes were sequenced and then tested in MLPA analysis. Sequencing data shows that the long MLPA probes were identical to the designed ones, indicating the long probes can be easily prepared with the new method, and the MPLA analysis data shows that the results of MPLA analysis with these long probes were as same accurate and specific as with ones prepared with other methods. The sequencing data was not presented in the research article (X.Y. Ling, G.M. Zhang, G. Pan, H. Long, Y.H. Cheng, C.Y. Xiang, L. Kang, F. Chen, Z.N. Chen, Preparing long probes by an asymmetric PCR-based approach for multiplex ligation-dependent probe amplification (MLPA), Anal. Biochem. (2015), 10.1016/j.ab.2015.03.031, in press), but the MLPA analysis data was converted into figure 4 and figure 5 of the research article.