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. 2016 Sep;204(1):35-42.
doi: 10.1534/genetics.116.191726. Epub 2016 Jul 20.

Fast-Flowering Mini-Maize: Seed to Seed in 60 Days

Morgan E McCaw  1 , Jason G Wallace  2 , Patrice S Albert  1 , Edward S Buckler  3 , James A Birchler  4
Affiliations

Fast-Flowering Mini-Maize: Seed to Seed in 60 Days

Morgan E McCaw et al. Genetics. 2016 Sep.

Abstract

Two lines of Zea mays were developed as a short-generation model for maize. The Fast-Flowering Mini-Maize (FFMM) lines A and B are robust inbred lines with a significantly shorter generation time, much smaller stature, and better greenhouse adaptation than traditional maize varieties. Five generations a year are typical. FFMM is the result of a modified double-cross hybrid between four fast-flowering lines: Neuffer's Early ACR (full color), Alexander's Early Early Synthetic, Tom Thumb Popcorn, and Gaspe Flint, followed by selection for early flowering and desirable morphology throughout an 11-generation selfing regime. Lines A and B were derived from different progeny of the initial hybrid, and crosses between Mini-Maize A and B exhibit heterosis. The ancestry of each genomic region of Mini-Maize A and B was inferred from the four founder populations using genotyping by sequencing. Other genetic and genomic tools for these lines include karyotypes for both lines A and B, kernel genetic markers y1 (white endosperm) and R1-scm2 (purple endosperm and embryo) introgressed into Mini-Maize A, and ∼24× whole-genome resequencing data for Mini-Maize A.

Keywords: Zea mays; flowering time; heterosis; maize; model system.

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Figures

Figure 1
Figure 1
FFMM-A and -B. A FFMM-A plant (left), and a FFMM-B plant (right) 30 days after planting. The flag leaves of the ears have been trimmed. Silks were present on the FFMM-A plant and were cut with the flag leaves. The nursery pots are ∼15 cm in diameter by ∼17 cm in depth, which is smaller than what is required for a normal maize plant.
Figure 2
Figure 2
Inferred ancestry along the FFMM chromosomes. Genotyping-by-sequencing was performed on four individuals of each of the four founder populations, and haplotype similarity was used to infer probable ancestry across the FFMM-A (panel A) and B (panel B) genomes. Colored blocks indicate a region probably inherited from the corresponding parent population; regions of ambiguous ancestry are colored gray, and sections shared between the two FFMM lines are considered identical by descent (IBD) and are highlighted along the sides in purple. The full similarity traces across each chromosome are in Figure S1. Alexander, Alexander’s Early Early Synthetic; Neuffer, Neuffer’s ACR.
Figure 3
Figure 3
Genome-size estimation. The nuclear genome content (c-value) of both FFMM lines, samples from the four founder populations, and several inbred lines were determined by flow cytometry. Each point is from a separate plant, except for the Alexander and Tom Thumb samples, which had only two plants each (and thus some plants were sampled multiple times). Samples are arranged in order of increasing median c-value.
Figure 4
Figure 4
Karyotype of FFMM-A and FFMM-B. Karyotypes of FFMM-A and FFMM-B using the protocol described in Kato et al. (2004) with modifications of the probes used, as described in the materials and methods section under the subheading “Karyotypes.” Red is Cent4, TAG, and subtelomere 1.1; green is CentC and subtelomere 4-12-1; blue is 180 bp Knob; white is TR-1 Knob; teal (green and blue) is NOR 173 ribosomal DNA; and yellow-orange (red and green) is 5S ribosomal DNA.
Figure 5
Figure 5
Ears produced in the heterosis trial. (A) FFMM-A from the warmer greenhouse, (B) FFMM-A from the cooler greenhouse, (C) FFMM-B from the warmer greenhouse, (D) FFMM-B from the cooler greenhouse, (E) hybrid from the warmer greenhouse, and (F) hybrid from the cooler greenhouse. The primary ear of each plant is arranged in a line along the bottom of each group; any additional ears from the same plant are aligned above the primary. Some additional ears were secondary ears while others were produced on tillers. All ears were openly pollinated with additional pollination performed by shaking pollen onto a sheet of paper and applying to the silks of the primary ear to ensure optimal seed set.
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