Abstract
The somatic regeneration of maize depends on its genotypes, so improving its variety with modern biotechnology is severely restricted. Locating the quantitative trait loci (QTLs) associated with somatic regeneration is important for breeding elite inbred lines that undergo genetic transformations. Here, by crossing the high-regeneration inbred line H99 and non-regeneration inbred line Fr993, an F2 population and its F2:3 and F2:4 population families were constructed. Immature embryos from the family populations were subjected to tissue culture in two independent seasons to determine their embryogenic callus induction rates (EIRs), green callus rates (GCRs) and plantlet regeneration rates (PRRs). Genetic linkage maps were constructed for the F2 population to locate somatic regeneration QTLs. The results showed that variation in the EIR, GCR and PRR ranged from 0.00–99.33%, and their broad-sense heritabilities were 0.50, 0.52 and 0.53, respectively. The total genetic distance of the linkage maps constructed by the GenoBaits 10 K chip was 2319.50 cM, and twelve QTLs were associated with somatic regeneration traits, accounting for 3.90–14.06% of the phenotypic variation. Expression analysis revealed six candidate genes screened from the QTLs with distinct responses to induction culture in the parental lines, suggesting that they may impact commitment to somatic cell fate. These results provide a basis for the molecular breeding of maize varieties with high-frequency somatic regeneration.
Highlights
The fate of maize somatic cells can be reprogrammed under the action of hormones and the cells allowed to develop into an independent complete plant through cell division and differentiation, which is the theoretical basis for establishing an efficient regeneration system
Since Green and Philips [1] first used immature maize embryos to induce callus and obtain regenerated plants in 1975, a large number of studies have found that embryogenic callus (EC) is difficult to induce in most maize genotypes and almost no elite inbred lines can regenerate as a result [2–4]; inbred lines do not serve as a direct recipient for foreign genes
The results showed that the broad-sense heritability of the somatic redifferentiation rate reached 0.75, and the number of plantlets regenerated from EC was as high as 0.74, which confirmed that the somatic regeneration of maize is mainly controlled by genetic factors and that it is feasible to further locate the major genes controlling this trait by molecular methods
Summary
The fate of maize somatic cells can be reprogrammed under the action of hormones and the cells allowed to develop into an independent complete plant through cell division and differentiation, which is the theoretical basis for establishing an efficient regeneration system. The genetic transformation of maize can be carried out using only a few lines, and the agronomic traits of these lines are suboptimal. If these materials are transformed for production, they must go through multiple generations of backcrossing, which greatly reduces their use value [5,6]. Somatic regeneration in maize is mainly divided into the organogenesis and somatic embryogenesis pathways. In both pathways, explant differentiation must be induced to obtain meristematic potential, and a meristem or embryonic developmentlike process occurs to form a complete plant. The growth state of donor plants and the culture conditions of explants have a certain impact on regenerated plant formation [10,11]
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