Maize has a long history of genetic and genomic tool development and is considered one of the most accessible higher plant systems. With a fully sequenced genome, a suite of cytogenetic tools, methods for both forward and reverse genetics, and characterized phenotype markers, maize is amenable to studying questions beyond plant biology. Major discoveries in the areas of transposons, imprinting, and chromosome biology came from work in maize. Moving forward in the post-genomic era, this classic model system will continue to be at the forefront of basic biological study. In this review, we outline the basics of working with maize and describe its rich genetic toolbox.
KEYWORDS genetics; genomics; maize; toolsWorking with Maize T HE term maize is often used synonymously with corn, particularly in the United States and in reference to its agricultural use. While both terms are correct, maize is a name that refers uniquely to this plant. Maize is a large grain plant that evolved from its wild-grass ancestors by the direct intervention of human agriculture. Many varieties or "races" differ in physical properties (Goodman and Brown 1988), but generally maize is a single-stalk plant that grows to approximately 8 feet tall with about 20 long, narrow leaves growing individually from nodes along the stalk (Figure 1A) (Kiesselbach 1999). Several characteristics make it an attractive genetic system (Strable and Scanlon 2009). It is easy to culture on any scale, from a few plants in pots to many acres ( Figure 1B). It can be grown successfully year round in greenhouses and growth chambers with proper lighting; it is also quite hardy and can be grown outdoors under a range of conditions, from tropical to temperate climates (Shaw 1988). Maize is a naturally outcrossing species, which makes its genetic architecture (diversity, linkage, recombination, etc.) more similar to other outcrossing organisms such as humans rather than self-pollinating plants ( Rafalski and Morgante 2004;Wallace et al. 2013). While its genetics are similar to humans, maize retains the major strength of plant genetics: the ability to self-cross and quickly produce homozygotes or F2 populations.The male and female reproductive organs are accessible and separable, making controlled crosses easy to perform. The male germ cells are produced in the tassel found at the top of the plant ( Figure 1C). Tassels contain anthers that open upon maturation, releasing up to 10 7 wind-dispersed pollen grains (Coe et al. 1988). The female germ cells are located in one or more ears, which grow from the base of leaves in the midsection of the plant (Figure 1, A and D). An ear generally contains several hundred egg cells that will develop into kernels after fertilization (Neuffer et al. 1997). Each young kernel contains a silk, an elongated stigma, which emerges out of the husk leaves of the ear ( Figure 1D). Pollen grains land on the silk and produce a pollen tube that grows down through the length of the silk, ultimately delivering two sperm to the female gametophy...