Abstract
Doubled haploid technology is highly successful in maize breeding programs and is contingent on the ability of maize inducers to efficiently produce haploids. Knowledge of the genes involved in haploid induction is important for not only developing better maize inducers, but also to create inducers in other crops. The main quantitative trait loci involved in maize haploid induction are qhir1 and qhir8. The gene underlying qhir1 has been discovered and validated by independent research groups. Prior to initiation of this study, the gene associated with qhir8 had yet to be recognized. Therefore, this research focused on characterizing positional candidate genes underlying qhir8. Pursuing this goal, a strong candidate for qhir8, GRMZM2G435294 (MYO), was silenced by RNAi. Analysis of crosses with these heterozygous RNAi-transgenic lines for haploid induction rate revealed that the silencing of MYO significantly enhanced haploid induction rate by an average of 0.6% in the presence of qhir1. Recently, GRMZM2G465053 (ZmDMP) was identified by map-based gene isolation and shown to be responsible for qhir8. While our results suggest that MYO may contribute to haploid induction rate, results were inconsistent and only showing minor increases in haploid induction rate compared to ZmDMP. Instead, reciprocal crosses clearly revealed that the silencing of MYO causes male sterility.
Highlights
Doubled haploid (DH) lines are created when cells of haploid seedlings undergo genome doubling, resulting in completely homozygous diploid offspring after self-pollination
While our results suggest that MYO may contribute to haploid induction rate, results were inconsistent and only showing minor increases in haploid induction rate compared to ZmDMP
Four out of five SNPs were at the third degenerate position of the codon sequence, all leading to silent mutations
Summary
Doubled haploid (DH) lines are created when cells of haploid seedlings undergo genome doubling, resulting in completely homozygous diploid offspring after self-pollination. Most haploids utilized in maize breeding programs are created by in vivo maternal haploid induction, which involves crossing a haploid inducer genotype as male to donor genotypes. Current inducers induce haploids at rates of >8% [1,2]. Genetic mechanisms controlling haploid induction rate (HIR) in maize are not well understood. Quantitative trait locus (QTL) mapping has located a major QTL on chromosome 1 [3,4]. The first comparative genome-wide QTL analysis involving inducers UH400 and CAUHOI confirmed that a major QTL, qhir, is present on chromosome 1, and a minor QTL, qhir, was found on chromosome
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