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Organization of the Prolamin Gene Family Provides Insight into the Evolution of the Maize Genome and Gene Duplications in Grass Species

1.       Jian-Hong Xu
<http://www.pnas.org/search?author1=Jian-Hong++Xu&sortspec=date&submit=Submit>  and

2.       Joachim Messing
<http://www.pnas.org/search?author1=Joachim++Messing&sortspec=date&submit=Submit> *


Author Affiliations

1.       Waksman Institute, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8020

1.        Communicated by Brian A. Larkins, University of Arizona, Tucson, AZ, July 29, 2008 (received for review April 9, 2008)


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.

*       allotetraploidy

*  centromere formation

*         chromosome structure

*         comparative genomics


*         *To whom correspondence should be addressed. E-mail:

*         Author contributions: J.-H.X. and J.M. designed research; J.-H.X. performed research; J.-H.X. and J.M. analyzed data; and J.-H.X. and J.M. wrote the paper.

*         The authors declare no conflict of interest.

*         (c) 2008 by The National Academy of Sciences of the USA