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Nature 443, E8-E9 (28 September 2006) | doi:10.1038/nature05252; Published online 27 September 2006

Increased outcrossing in hothead mutants (Reply)

Susan J. Lolle1, Robert E. Pruitt2, J. L. Victor2 and J. M. Young2

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Arising from: S. J. Lolle, J. L. Victor, J. M. Young & R. E. Pruitt Nature 434, 505–509 (2005).

The results obtained by Peng et al.1 are consistent with an increased amount of outcrossing in hth mutants of Arabidopsis thaliana. Some of the results, such as the acquisition of a novel transgene, would be difficult to explain by any other mechanism. Outcrossing was a possibility that we thoroughly explored early on in our investigation2, but we discounted it as an explanation because it was inconsistent with many of our experimental results.

We described two experiments that were inconsistent with outcrossing2: one in which there was transmission of a wild-type HTH allele from a homozygous mutant (hth/hth) male parent, and another in which there was recovery of homozygous wild-type (HTH/HTH) embryos dissected from homozygous mutant (hth/hth) parents. In further experiments that were similar, but not identical, to those described by Peng et al.1, we did see reversion in hth/hth homozygotes grown in isolation (results not shown).

These results together indicate that the genetic events that we see in hth mutants cannot be explained solely by outcrossing, but they do not rule out the possibility that outcrossing could be increased relative to that occurring in the wild type. The lower frequency of reversion seen when pollen from an hth/hth parent is used to pollinate a wild-type female may reflect elimination of these outcrossing events.

We have also examined more extensive patterns of inheritance of single-nucleotide polymorphisms in F2 populations, similar to those we originally described2. These patterns of inheritance are also inconsistent with an outcrossing explanation because there was no single male parent present that could have provided the combination of non-parental alleles observed in the 'restored' progeny. Furthermore, the results indicate that genetic restoration of ancestral alleles can take place in HTH/hth heterozygotes; these plants have a floral morphology identical to wild type and therefore would not be expected to show increased outcrossing (J.M.Y., R.E.P. and S.J.L., unpublished results).

In summary, the outcrossing explanation proposed by Peng et al.1 is a reasonable hypothesis to explain some of the data associated with hothead genetics, and indeed is one of the first that we considered. Ultimately, we discarded this explanation because it was inconsistent with many of our experimental results. However, the results of Peng et al. show that, at least under some growth conditions, outcrossing in hth/hth plants remains an issue that needs to be taken into account.

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  1. Peng, P., Chan, S. W.-L., Shah, G. A. & Jacobsen, S. E. Nature 443, doi: 10.1038/nature05251 (2006).
  2. Lolle, S. J., Victor, J. L., Young, J. M. & Pruitt, R. E. Nature 434, 505–509 (2005). | Article | PubMed | ISI | ChemPort |
  1. Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
  2. Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907-2054, USA

Correspondence to: Robert E. Pruitt2 Email: