A Complete Set of Maize Individual Chromosome Additions to the Oat Genome

Abstract

All 10 chromosomes of maize (Zea mays, 2n ϭ 2x ϭ 20) were recovered as single additions to the haploid complement of oat (Avena sativa, 2n ϭ 6x ϭ 42) among F 1 plants generated from crosses involving three different lines of maize to eight different lines of oat. In vitro rescue culture of more than 4,300 immature F 1 embryos resulted in a germination frequency of 11% with recovery of 379 F 1 plantlets (8.7%) of moderately vigorous growth. Some F 1 plants were sectored with distinct chromosome constitutions among tillers of the same plant and also between root and shoot cells. Meiotic restitution facilitated development of un-reduced gametes in the F 1. Self-pollination of these partially fertile F 1 plants resulted in disomic additions (2n ϭ 6x ϩ 2 ϭ 44) for maize chromosomes 1, 2, 3, 4, 6, 7, and 9. Maize chromosome 8 was recovered as a monosomic addition (2n ϭ 6x ϩ 1 ϭ 43). Monosomic additions for maize chromosomes 5 and 10 to a haploid complement of oat (n ϭ 3x ϩ 1 ϭ 22) were recovered several times among the F 1 plants. Although partially fertile, these chromosome 5 and 10 addition plants have not yet transmitted the added maize chromosome to F 2 offspring. We discuss the development and general utility of this set of oat-maize addition lines as a novel tool for maize genomics and genetics.

Maize centromeres expand and adopt a uniform size in the genetic background of oat

“…We postulate that the transcription of these large genes impedes the expansion of CENH3 domains, similar to barriers that block the spreading of heterochromatin (Noma et al 2006;Scott et al 2006). Some maize chromosomes were especially difficult to recover in oat-maize hybrids (Kynast et al 2001;Rines et al 2009), suggesting that the expansion of centromeres may have failed. For example, maize chromosome 3 was not recovered from the oat 3 B73 and oat 3 Mo 17 hybrids.…”

“…Oat-maize chromosome addition line OMA3.01 contains maize chromosome 3 derived from maize hybrid Seneca 60 (Kynast et al 2001). The oat-maize neoM3 monosomic addition line was derived from OMA3.01 (Topp et al 2009).…”

“…Two of the most distant plant species to ever be crossed are oat (Avena sativa, 2n = 63 = 42) and maize (Zea mays, 2n = 23 = 20), which diverged nearly 60 million years ago. Most of the maize chromosomes are stochastically lost in progeny, often retaining just one maize chromosome in the oat background (Kynast et al 2001). Since the oat genome (11,300 Mb) is over four times bigger than the maize genome (2500 Mb), and total (summed) centromere size scales linearly with genome size (Zhang and Dawe 2012), we predicted that maize centromeres would expand in the oat background.…”

Individual Maize Chromosomes in the C3 Plant Oat Can Increase Bundle Sheath Cell Size and Vein Density

“…Interestingly, two of the lines showing reduced vein spacing are derived from crosses involving oat sun II as the recipient, implying that the genetic background of sun II may be more receptive to alterations in vein spacing. The difficulty of generating stable double and triple OMA lines (Kynast et al, 2001) means that testing the additive effects of chromosomes 1, 5, and 9 is not trivial.…”

“…To address this question, we used oat 3 maize addition lines (OMAs) to test if determinants of Kranz anatomy from maize were functional in a C 3 leaf. OMAs are oat (Avena sativa) plants with individual maize chromosomal additions to the oat genome (Riera-Lizarazu et al, 1996Kynast et al, 2001). OMAs allow the effects of individual maize (C 4 ) chromosomes to be considered within a C 3 context, substantially reducing the complexity of the maize genome and permitting traits of interest to be mapped to individual chromosomes (Riera-Lizarazu et al, 2000).…”