David Braun

Alleles of afd1 dissect REC8 functions during meiotic prophase I

REC8 is a master regulator of chromatin structure and function during meiosis. Here, we dissected the functions of absence of first division (afd1), a maize rec8/α-kleisin homolog, using a unique afd1 allelic series. The first observable defect in afd1 mutants is the inability to make a leptotene chromosome. AFD1 protein is required for elongation of axial elements but not for their initial recruitment, thus showing that AFD1 acts downstream of ASY1/HOP1. AFD1 is associated with the axial and later the lateral elements of the synaptonemal complex. Rescuing 50% of axial element elongation in the weakest afd1 allele restored bouquet formation demonstrating that extent of telomere clustering depends on axial element elongation. However, rescuing bouquet formation was not sufficient for either proper RAD51 distribution or homologous pairing. It provides the basis for a model in which AFD1/REC8 controls homologous pairing through its role in axial element elongation and the subsequent distribution of the recombination machinery independent of bouquet formation.

Utility and distribution of conserved noncoding sequences in the grasses

Control of gene expression requires cis-acting regulatory DNA sequences. Historically these sequences have been difficult to identify. Conserved noncoding sequences (CNSs) have recently been identified in mammalian genes through cross-species genomic DNA comparisons, and some have been shown to be regulatory sequences. Using sequence alignment algorithms, we compared genomic noncoding DNA sequences of the liguleless1 (lg1) genes in two grasses, maize and rice, and found several CNSs in lg1. These CNSs are present in multiple grass species that represent phylogenetically disparate lineages. Six other maize/rice genes were compared and five contained CNSs. Based on nucleotide substitution rates, these CNSs exist because they have biological functions. Our analysis suggests that grass CNSs are smaller and far less frequent than those identified in mammalian genes and that mammalian gene regulation may be more complex than that of grasses. CNSs make excellent pan-grass PCR-based genetic mapping tools. They should be useful as characters in phylogenetic studies and as monitors of gene regulatory complexity.

Biodiversity (Communications arising): Maize transgene results in Mexico are artefacts (see editorial footnote)

Quist and Chapelas conclusion that the transgenes they claim to have detected in native maize in Oaxaca, Mexico, are predominantly reassorted and inserted into a “diversity of genomic contexts” seems to be based on an artefact arising from the inverse polymerase chain reaction (i-PCR) they used to amplify sequences flanking 35S transgenes from cauliflower mosaic virus (CaMV).

Biodiversity (Communications arising): maize transgene results in Mexico are artefacts.

Quist and Chapelas conclusion that the transgenes they claim to have detected in native maize in Oaxaca, Mexico, are predominantly reassorted and inserted into a “diversity of genomic contexts” seems to be based on an artefact arising from the inverse polymerase chain reaction (i-PCR) they used to amplify sequences flanking 35S transgenes from cauliflower mosaic virus (CaMV).

Maize transgene results in Mexico are artefacts (see editorial footnote): Biodiversity (Communications arising)

Quist and Chapelas conclusion that the transgenes they claim to have detected in native maize in Oaxaca, Mexico, are predominantly reassorted and inserted into a “diversity of genomic contexts” seems to be based on an artefact arising from the inverse polymerase chain reaction (i-PCR) they used to amplify sequences flanking 35S transgenes from cauliflower mosaic virus (CaMV).