QTL Mapping for Haploid Inducibility Using Genotyping by Sequencing in Maize.

Doubled haploid (DH) technology in maize takes advantage of in vivo haploid induction (HI) triggered by pollination of donors of interest with inducer genotypes. However, the ability of different donors to be induced-inducibility (IND), varies among germplasm and the underlying molecular mechanisms are still unclear. In this study, the phenotypic variation for IND in a mapping population of temperate inbred lines was evaluated to identify regions in the maize genome associated with IND. A total of 247 F2:3 families derived from a biparental cross of two elite inbred lines, A427 and CR1Ht, were grown in three different locations and Inclusive Composite Interval Mapping (ICIM) was used to identify quantitative trait loci (QTL) for IND. In total, four QTL were detected, explaining 37.4% of the phenotypic variance. No stable QTL was found across locations. The joint analysis revealed QTL × location interactions, suggesting minor QTL control IND, which are affected by the environment.

QTL mapping of spontaneous haploid genome doubling using genotyping-by-sequencing in maize (Zea mays L.).

KEY MESSAGE: A major QTL for SHGD was identified on chromosome 5 with stable expression across environments. The introgression this QTL can overcome the need of colchicine in DH lines development. Genome doubling of haploids is one of the major constraints of large-scale doubled haploid (DH) technology. Improving spontaneous haploid genome doubling (SHGD) is an alternative to overcome this limitation. In this study, we aimed to construct a high-density linkage map based on genotyping by sequencing of single nucleotide polymorphism, to detect QTL and QTL by environment (Q by E) interactions affecting SHGD and to identify the best trait for mapping and selection of haploid male fertility (HMF). To this end, a biparental population of 220 F2:3 families was developed from a cross between A427 (high HMF) and CR1Ht (moderate HMF) to be used as donor. A high-density linkage map was constructed containing 4171 SNP markers distributed over 10 chromosomes with an average distance between adjacent markers of 0.51 cM. QTL mapping for haploid fertile anther emergence, pollen production, tassel size, and HMF, identified 27 QTL across three environments, and Q by E interactions were significant. A major QTL was identified on chromosome 5. This QTL explained over 45% of the observed variance for all traits across all environments. The introgression of this major QTL, using marker-assisted backcrossing, has great potential to overcome the need of using colchicine in DH line development.

Mapping of QTL and identification of candidate genes conferring spontaneous haploid genome doubling in maize (Zea mays L.).

In vivo doubled haploid (DH) technology is widely used in commercial maize (Zea mays L.) breeding. Haploid genome doubling is a critical step in DH breeding. In this study, inbred lines GF1 (0.65), GF3(0.29), and GF5 (0) with high, moderate, and poor spontaneous haploid genome doubling (SHGD), respectively, were selected to develop mapping populations for SHGD. Three QTL, qshgd1, qshgd2, and qshgd3, related to SHGD were identified by selective genotyping. With the exception of qshgd3, the source of haploid genome doubling alleles were derived from GF1. Furthermore, RNA-Seq was conducted to identify putative candidate genes between GF1 and GF5 within the qshgd1 region. A differentially expressed formin-like protein 5 transcript was identified within the qshgd1 region.

Novel technologies in doubled haploid line development.

haploid inducer line can be transferred (DH) technology can not only shorten the breeding process but also increase genetic gain. Haploid induction and subsequent genome doubling are the two main steps required for DH technology. Haploids have been generated through the culture of immature male and female gametophytes, and through inter- and intraspecific via chromosome elimination. Here, we focus on haploidization via chromosome elimination, especially the recent advances in centromere-mediated haploidization. Once haploids have been induced, genome doubling is needed to produce DH lines. This study has proposed a new strategy to improve haploid genome doubling by combing haploids and minichromosome technology. With the progress in haploid induction and genome doubling methods, DH technology can facilitate reverse breeding, cytoplasmic male sterile (CMS) line production, gene stacking and a variety of other genetic analysis.