Rice Genetics IV - IRRI books - International Rice Research Institute

sequenced the two rice DMC1 genes and compared their exons, introns, and promotersfor conservation of sequence. The exons were highly conserved whereas the intronswere divergent. This result establishes that both copies of the gene are functionaland under selection for protein structure. Both DMC1 genes are expressed inpanicles at the time of meiosis and in roots and calli. In addition, DMC1B is expressedin the pollen during mitosis; it is also expressed in the embryo. Consistentwith such differential expression, the promoter regions of the two genes and that ofbarley DMC1 show only partial conservation. We are focusing on the promoter ofDMC1A because of its more limited pattern of expression. We have made promotergusfusions and promoter mutations to determine whether any of the conserved promoterelements are capable of conferring meiosis-specific expression. We shall alsouse these constructs to determine whether the promoter of DMC1A is expressed inany tissues in the developmental cycle leading from nucellus to nucellus in the plannedapomict. If root tips are the only sites where DMC1A is expressed mitotically, thepromoter should be usable directly to promote correct activation of cre recombinase.Conclusion: integrating apomixis into rice breeding programsNaturally occurring apomicts are either obligate or facultative. Agriculturally successfulapomicts of rice, by contrast, will have to be inducible, with breeders beingable to control the switch between the sexual and asexual pathways of reproduction.Apomixis is useful because it fixes the genotype of elite cultivars but sexuality isuseful for making further improvements as changing circumstances may require. Evenwhen naturally occurring apomixis genes become available, this sort of control willbe desirable. For this reason, it is highly likely that all commercial forms of apomixiswill involve some degree of genetic engineering.If apomixis were available in hybrid rice, breeders could conduct hybridizationmanually and then multiply the apomictic hybrid seed cheaply in the field. At present,they must conduct inefficient field-scale hybridization. Farmers would be able to reproduceapomictic hybrid seed in their own fields and so would not need to purchasefresh seed every season. The advantages of hybrid rice would thus become availableto poor farmers.ReferencesAsker S, Jerling L. 1992. Apomixis in plants. Boca Raton, Fla. (USA): CRC Press.Barcaccia G, Mazzucato A, Albertini E, Zethof J, Gerats A, Pezzotti M, Falcinelli M. 1998.Inheritance of parthenogenesis in Poa pratensis L.: auxin test and AFLP linkage analysessupport monogenic control. Theor. Appl. Genet. 97:74-82.Bennett J, Ladha JK, Schmit V, Sheehy J. 1998. New Frontier Projects: beyond the pipeline. In:Dowling NG, Greenfield SM, Fischer KS, editors. Sustainability of rice in the global foodsystem. Manila (Philippines): International Rice Research Institute. p 225-243.Bicknell RA. 1997. Isolation of a diploid, apomictic plant of Hieracium aurantiacum. SexualPlant Reprod. 10:168-172.396 Bennett et al