Organization of the prolamin gene family provides insight into the evolution of the maize genome and gene duplications in grass species.
Proc Natl Acad Sci U S A. 105:14330-5. Abstract
Zea mays, commonly known as corn, is perhaps the most greatly produced crop in terms of tonnage and a major food, feed, and biofuel resource. Here we analyzed its prolamin gene family, encoding the major seed storage proteins, as a model for gene evolution by syntenic alignments with sorghum and rice, two genomes that have been sequenced recently. Because a high-density gene map has been constructed for maize inbred B73, all prolamin gene copies can be identified in their chromosomal context. Alignment of respective chromosomal regions of these species via conserved genes allow us to identify the pedigree of prolamin gene copies in space and time. Its youngest and largest gene family, the alpha prolamins, arose about 22-26 million years ago (Mya) after the split of the Panicoideae (including maize, sorghum, and millet) from the Pooideae (including wheat, barley, and oats) and Oryzoideae (rice). The first dispersal of alpha prolamin gene copies occurred before the split of the progenitors of maize and sorghum about 11.9 Mya. One of the two progenitors of maize gained a new alpha zein locus, absent in the other lineage, to form a nonduplicated locus in maize after allotetraplodization about 4.8 Mya. But dispersed copies gave rise to tandem duplications through uneven expansion and gene silencing of this gene family in maize and sorghum, possibly because of maize's greater recombination and mutation rates resulting from its diploidization process. Interestingly, new gene loci in maize represent junctions of ancestral chromosome fragments and sites of new centromeres in sorghum and rice.
Organization and variability of the maize genome.
Current opinion in plant biology. 9:157-63. Abstract
With a size approximating that of the human genome, the maize genome is about to become the largest plant genome yet sequenced. Contributing to that size are a whole-genome duplication event and a retrotransposition explosion that produced a large amount of repetitive DNA. This DNA is greatly under-represented in cDNA collections, so analysis of the maize transcriptome has been an expedient way of assessing the gene content of maize. Over 2 million maize cDNA sequences are now available, making maize the third most widely studied organism, behind mouse and man. To date, the sequencing of large-sized DNA clones has been largely driven by the genetic interests of different investigators. The recent construction of a physical map that is anchored to the genetic map will aid immensely in the maize genome-sequencing effort. However, studies showing that the repetitive DNA component is highly polymorphic among maize inbred lines point to the need to sample vertically a few specific regions of the genome to evaluate the extent and importance of this variability.