Ac transposable element induction and behavior in immature maize embryo cultures, seeds and pollen treated with caffeine, 5-azacytidine, 1-beta-D-arabinofuranosylcytosine and ethyl methanesulfonate
Abstract
Hybrid seed corn production in the United States relies on a limited number of elite inbreds. The objective was to increase genetic variability by generating isolines through induction and control of the Ac transposable element. Chemical effects on induction of the Ac transposable element were studied in immature maize embryo cultures, mature seeds and pollen. Genotypes included A188 x W22 bz-m2 (DsI or DsII) derivatives, W22 bz-m2 (DsI), A188 x H99 hybrids and derivatives, inbreds A188, H99 and Pa91, and the DsC tester and its A188 hybrid. Caffeine, 5-azacytidine (5AC) or 5-aza-2$\sp\prime$-deoxycytidine (d5AC) and ethyl methanesulfonate (EMS) had little effect on Ac induction in maize seeds and pollen. No Ac induction was detected in 425 inbred regenerants (R$\sb0$), 320 F$\sb1$-derived R$\sb0$ and 213 F$\sb2$ or F$\sb3$-derived R$\sb0$ plants. One Ac induction event occurred in 36 R$\sb0$ plants from A188 x W22 bz-m2 (DsI) F$\sb2$ sib-pollinated or F$\sb3$-derived lines. Ac induction was too low to be generally useful for isoline development. Ac transposable element behavior was studied in embryo cultures, seeds and pollen treated with the above chemicals in W22 bz-m2 isolines and A188 x W22 bz-m2 derivatives for Ac, DsI and DsII. Models for Ac transposition and mitotic segregation of unlike products indicated that Ac transposition occurred in 60 to 90% of the 303 R$\sb0$ plants. Such increased Ac transposition may enhance transposon tagging of genes. One d5AC somaclone of nine R$\sb0$ plants from the same callus uniquely segregated for the dull gene and for Ac transposition. While caffeine, d5AC and AraC had no apparent effect on this variability arising from culture, caffeine and EMS induced significant numbers of early Ac transposition events in treated embryos. AraC posttreatments increased the magnitude of EMS effects. Caffeine, d5AC and AraC had no observable effect on Ac in pollen mutagenesis. Because of known effects by AraC and caffeine on DNA repair mechanisms, it is postulated that the precocious transposition is due to repair events themselves or to rearrangements in repetitive DNA sequences with resultant changes in cytosine methylation patterns. Caffeine, 5AC and AraC were observed to have effects on immature embryo callus morphology.
Degree
Ph.D.
Advisors
Glover, Purdue University.
Subject Area
Agronomy|Genetics|Plant propagation
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