5-azacytidine induces chromosomal breakage in the root tips of wheat carrying the cuckoo chromosome 4S(L) from Aegilops sharonensis

Jose I. de las Heras, Ian P. King, John S. Parker

Research output: Contribution to journalArticlepeer-review

Abstract

Gametocidal or `cuckoo' chromosomes have been found in a number of Aegilops species (for a review see Endo, 1990). Cuckoo chromosomes are preferen- tially transmitted when introduced by hybridization into common wheat, Triticum aestivum (2n 6x 42, AABBDD). When present in the sporophyte, gameto- cidal (Gc) factors in the cuckoo chromosomes induce chromosomal breakage in the gametes not containing them, ensuring their own transmission to the progeny (Finch et al., 1984; Nasuda et al., 1998). Plants carry- ing Gc factors in the hemi- or heterozygous form are semi-sterile. However, plants homozygous for Gc fac- tors are fully fertile. Mutations such as deletions and other rearrangements have been detected among the progeny of plants hemi- or heterozygous for the Gc factors. These are thought to arise from gametes that do not carry the Gc gene(s) and su er chromosomal breakage at levels that are not lethal (Endo, 1988a,b, 1990). This phenomenon has been employed to pro- duce sets of deletion stocks in the common wheat cultivar Chinese Spring (CS), using the cuckoo chro- mosome 2C from Ae. cylindrica (Endo&Gill, 1996). The mechanism inducing the chromosomal aberrations is not understood. The cuckoo chromosome 4SL from Ae. sharonensis (2n 2x 14, SLSL) has a very strong gametocidal action in CS and other wheat cultivars (King et al., 1991). Chromosome fragments, usually in the form of pairs of equal length single chromatid segments (SCSs), have been observed during early embryo and endo- sperm development of plants carrying cuckoo chromo- somes (King & Laurie, 1993; de las Heras, 1999). Broken chromosome ends exhibit a tendency to fuse and form dicentric chromosomes (McClintock, 1941; Werner et al., 1992). These dicentrics usually give rise to chromatin bridges at anaphase and may break at telophase, thus perpetuating the break±fusion±bridge (BFB) cycle after fusion of the newly broken chromo- some ends. The mechanism for the Gc-induced chromosomal damage appears to be switched o early during embryo and endosperm development (King & Laurie, 1993; de las Heras, 1999). Root tips from plants carrying the 4SL cuckoo chromosome do not show chromosome fragmentation. However, dicentric chromosomes are sometimes observed, presumably resulting from chro- mosome fragmentation during late gametogenesis and/ or early embryogenesis. In the work presented here we demonstrate that the DNA hypomethylating agent 5-azacytidine (5-AC) induces chromosomefragmentation in the root tips of plants carrying the cuckoo chromo- some 4SL, but not in plants lacking this chromosome.
Original languageEnglish
Pages (from-to)474-479
Number of pages6
JournalHeredity
Volume87
Issue number4
DOIs
Publication statusPublished - 2001

Keywords

  • 5-azacytidine
  • Aegilops sharonensis
  • BFB cycles
  • chromosome breakage
  • DNA methylation
  • gametocidal chromosomes

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