Stocks carrying mapped Ac elements available from the Co-op
-- Hugo K. Dooner
Several recently developed Ac-carrying stocks have been deposited with the Stock Center. These stocks carry Ac elements that have been mapped to chromosomes or chromosome arms and, therefore, constitute potentially useful starting materials for transposon tagging experiments.
Last summer, seed was generated from 24 stocks carrying different Acs that transposed from bz-m2(Ac) in 9S to non-9 sites in the genome (Dooner et al., Genetics 136:261-279, 1994). Many of these Acs are in chromosomes or chromosome arms for which no mutable alleles carrying Ac are known. Each transposed Ac (trAc) was re-extracted from the particular translocation with which it originally showed linkage and its linkage to wx, the translocation breakpoint marker, was verified. A fair supply of seed for each trAc (from 30 to 50 semisterile ears) has been sent to the Stock Center. The Stock Center needs to regrow these stocks and assign them new numbers, but is prepared to handle some seed requests in 1995.
The seeds deposited with the Co-op derive from the particular translocation
heterozygote in the wx translocation series that showed linkage
between wx (the T breakpoint) and Ac. The bz-m
seeds are segregants from crosses of the type
Bz wx-T +
bz Wx-N Ac x bz-m2(DI) wx (no Ac)
and should therefore be bz Wx/ bz-m2(DI) wx ; Ac/+, i.e., they should not carry the translocation and should not be semisterile. Also, barring undetectable double crossovers, they should carry the W22 parental contributions for both the bz Wx 9S segment and the segment in the non-9 chromosome extending from the position of the translocation breakpoint to that of the trAc.
Caveat. Since Ac does not reside in a reporter gene, a secondary transposition from its original location would not be easily detected. Therefore, some precautions need to be taken in propagating the stocks. Here are two suggested ways of proceeding.
(1) Amplify the stock by selfing the bz Wx/ bz-m2(DI) wx; Ac/+ plants. Then, pool the spotted seeds from several ears for use as Ac-carrying parents in the large scale tagging crosses the following generation. This procedure minimizes the problem of secondary transpositions by avoiding the bottleneck of using one or two plants, but results in plants carrying variable doses of Ac. It is the "quick and dirty" way.
(2) The safest procedure is to maintain the stock by crossing the bz Wx/ bz-m2(DI) wx; Ac/+ plants to the particular wx (Bz) translocation (available from the Stock Center) that showed linkage to the trAc in question. Then, take Wx segregants from the outcross and testcross them to the reporter stock bz-m2(DI) wx to confirm the Wx-Ac linkage. Keep ears showing linkage (most of the bronze seeds have spots) and discard the rare cases where a secondary transposition to an unlinked site has taken place (half of the bronze seeds have spots, half don't). This approach is more laborious and time consuming, but it gives one the added confidence that the individuals that one is using in the large scale tagging experiment descend from a plant that, in fact, had Ac in the targeted chromosome.
Table 1 lists the trAc stocks available, pertinent mapping information, and the chromosomal location of each trAc.
Table 1. List of transposed Ac maize stocks.
|trAc||Recent pedigree number||Translocation||Breakpt. in non9||Ac-wx (cM)1||Other information||Most likely location|
|6076 *||C4320||5-9a||5L.69||31||Ac-pr: 12cM||5L|
|8181||C4332-33||5-9a||5L.69||10||Ac-pr: 41 cM||5L|
* trAc is borne on a wx chromosome. The Ac-wx distance was determined directly from a Wx reciprocal translocation for 6076 and indirectly from the Ac-bz distance in a wx reciprocal translocation for 8162.
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