Rice Genetics IV - IRRI books - International Rice Research Institute

The life cycle of angiosperms is punctuated by a dormant phase that separatesembryonic and postembryonic development of the sporophyte. In the pickle (pkl)mutant of Arabidopsis, embryonic traits are expressed after germination (Ogas et al1999). The penetrance of the pkl phenotype is strongly enhanced by inhibitors ofgibberellin biosynthesis. Map-based cloning of the PKL locus revealed that it encodesa CHD3 protein. CHD3 proteins have been implicated as chromatin-remodelingfactors involved in repression of transcription. PKL is necessary for repression ofLEC1. Ogas et al (1999) proposed that PKL is a component of a gibberellin-modulateddevelopmental switch that functions during germination to prevent reexpressionof the embryonic developmental state.We have isolated a LEC1 homologue from rice. It is specifically expressed inresponse to fertilization and is most abundantly expressed 2–5 DAF (Fig. 7). It is notexpressed in panicles before flowering or in leaves, roots, or embryogenic calli. Theabsence of transcripts of this LEC1-like gene in calli is intriguing, because it suggeststhat the gene is not active in somatic embryos and is therefore involved in eventsunique to zygotic embryogenesis. In situ hybridization shows that the LEC1-like geneis highly expressed in zygotic embryos and in endosperm. We have also isolated asecond LEC1 homologue that is expressed in both zygotic and somatic embryos. Weshall compare the effectiveness of both LEC1 homologues to induce ectopic embryogenesis.–2 0 1 2 3 4 5 8Days afterfertilizationLEC1PKLFig. 7. RT-PCR shows the inverse relationship between transcript levels for LEC1 and PKLgenes in rice spikelets after flowering. LEC1 transcripts are most abundant and PKL transcriptsare least abundant at about 3 days after fertilization.Molecular tools for achieving synthetic apomixis in hybrid rice 393