THE MAIZE TRANSPOSABLE ELEMENT AC IS MOBILE IN THE LEGUME LOTUS-JAPONICUS

To evaluate the prospects for transposon mutagenesis in the autogamous diploid legume Lotus japonicus, the behaviour of the maize transposab le element Ac was analysed in the progeny;of 38 independent transgenic plants. The conditions for monitoring donor site excision using histo chemical localization of beta-glucuronidase activity or the alternativ e spectinomycin resistance assay were established, and used to follow Ac mobility through two generations. Somatic excision was monitored as variegated cotyledons in the T-2 generation and germinal excision eve nts were scored in segregating T-3 families as complete beta-glucuroni dase-mediated staining of cotyledons or as a fully green spectinomycin -resistant phenotype. Using these assays an average germinal excision frequency of 12% was estimated in the T-3 offspring from variegated pl ants. The fidelity of the excision assays was ascertained by comparing the frequency of germinal excision to the frequency of Ac reinsertion at new positions of the genome. Transposition of Ac in 42% of the pla nts and detection of the characteristic Ac insertion/excision footprin ts suggests that insertion mutagenesis with the autonomous maize Activ ator element is feasible in Lotus japonicus. Parameters influencing Ac behaviour, such as dosage, position effects and modification of the e lement itself, were also investigated comparing homozygous and hemizyg ous plants from the same family and by analysing different transforman t.