Chapter 5 Genetic Analysis of Apomixis - cimmyt

I.d,dio. of Apomilis i. I..ual PIa.,s by MI'age••sls 227pseudogamy can be concluded from theinduction of haploid parthenogenesis at highfrequency by the application of brassinolide,the steroid hormone present in pollen that maybe the trigger for endosperm developmentfollowing normal pollination (Kitani 1994).The fact that to date mutagenesis has notresulted in fertile maternal seed confirms thehypothesis that viable apomixis can only beobtained in species that have acquired thenecessary preadaptations. A long-termconsideration in our pursuit of apomicticmutants in Arabidopsis may well be to combinemutations obtained from different screeningprocedures. For example, it is possible that amutation that produces unreduced embryosacs, in combination with a ftslfie mutation(perhaps in the heterozygous state), wouldresult in a viable form of apomixis. Althoughsuch experiments could be carried out withoutfurther knowledge of the genes involved, animportant step toward a controllable systemof apomixis will be the isolation andcharacterization of the mutations and theirwild type alleles. The mutant genes could betransferred to normal Arabidopsis via T-DNA,to determine what effect they have in abackground where the wild type allele is alsopresent. It would be interesting to determineif the ftslfie mutations are transmissible byfemale gametes and, if dominant, give rise toseeds with autonomous endosperm andembryos.Efforts to identify apomixis genes from Arabis,as well as other apomicts, should eventuallycome to fruition. An intriguing area of inquiry,when that comes to pass, will be the nature ofthe relationship between these naturalapomixis loci and any mutations conferringapomictic characteristics that have beenidentified in the related sexual species. Thecombined strategies of mutagenesis in sexualplants to induce apomixis, and in apomicticplants to identify natural apomixis genes,should eventually enable us to understand theregulation of these traits and to manipulatethem in the best interests of agriculture.ReferencesAarts, M.G.M., P. Carzaan, WJ. Stiekema, and A. Pereira. 1995. Atwaelement Enhancer· Inhibitor transposon system in Arabidopsisthaliana. Mol. Gen. Genet. 247: 555-64.Ahokos, H. 1977. Amutont of barley: Triploid indu