Reciprocal chromosome translocation associated with TDNA-insertion mutation in Arabidopsis: genetic and cytological analyses of consequences for gametophyte development and for construction of doubly mutant lines

Abstract

Chromosomal rearrangements may complicate construction of Arabidopsis with multiple TDNA-insertion mutations. Here, crossing two lines homozygous for insertions in AtREV3 and AtPOLH (chromosomes I and V, respectively) and selfing F1 plants yielded non-Mendelian F2 genotype distributions: frequencies of +/++/+ and 1/1 2/2 progeny were only 0.42 and 0.25%. However, the normal development and fertility of double mutants showed AtPOLH-1 and AtREV3-2 gametes and 1/1 2/2 embryos to be fully viable. F2 distributions could be quantitatively predicted by assuming that F1 selfing produced inviable (1,2) and (+,+) gametophytes 86% of the time. Some defect intrinsic to the F1 selfing process itself thus appeared responsible. In selfing AtREV3 +/2 single mutants, imaging of ovules and pollen showed arrest or abortion, respectively, of half of gametophytes; however, gametogenesis was normal in AtREV3 2/2 homozygotes. These findings, taken together, suggested that T-DNA insertion at AtREV3 on chromosome I had caused a reciprocal I–V translocation. Spreads of meiosis I chromosomes in selfing AtREV3 +/2 heterozygotes revealed the predicted cruciform four-chromosome structures, which fluorescence in situ hybridization showed to invariably include both translocated and normal chromosomes I and V. Sequencing of the two junctions of T-DNA with AtREV3 DNA and the two with gene At5g59920 suggested translocation via homologous recombination between independent inverted-repeat T-DNA insertions. Thus, when crosses between TDNA-insertion mutants yield anomalous progeny distributions, TDNA-linked translocations should be considered.

TheArabidopsisDynamin-Related Protein2 Family Is Essential for Gametophyte Development

“…These mutants are the F1 progeny of crosses between wild-type Landsberg erecta plants and seven independent Salk insertional alleles that display pollen lethality upon outcrossing. This lethality is likely due to reciprocal chromosomal translocations in the parental Salk allele that cause 50% of the outcrossed pollen to have large chromosomal deletions that lead to pollen lethality, as has been previously described (Curtis et al, 2009). …”

Proper Levels of the Arabidopsis Cohesion Establishment Factor CTF7 Are Essential for Embryo and Megagametophyte, But Not Endosperm, Development

“…7, A-H) support this hypothesis and are consistent with another report showing that the 35S promoter is active during female gametophyte development (Liu et al, 2008). An alternative possibility, that the observed female gametophyte arrest results from chromosomal rearrangements associated with T-DNA insertion (Ray et al, 1997;Curtis et al, 2009), is less likely given the absence of pollen defects, the results of our expression studies, and the multiple independent occurrences of the phenotype in the transgenic lines.…”

The Fanconi Anemia Ortholog FANCM Ensures Ordered Homologous Recombination in Both Somatic and Meiotic Cells in Arabidopsis

“…If a translocation occurred, 50% of pollen should be inviable (Curtis et al, 2009), which we tested by esterase activity staining with fluorescein diacetate (Heslop-Harrison and Heslop-Harrison, 1970). None of the three fancm mutant lines showed pollen viability in the range of 50%.…”