Transposition of the maize transposable element Ac in barley (Hordeum vulgare L.).

Transposition of the maize autonomous element Ac (Activator) was investigated in barley (Hordeum vulgare L.) with the aim of developing a transposon tagging system for the latter. The Ac element was introduced into meristematic tissue of barley by microprojectile bombardment. Transposon activity was then examined in the resulting transgenic plants. Multiple excision events were detected in leaf tissue of all plant lines. The mobile elements generated empty donor sites with small DNA sequence alterations, similar to those found in maize. Reintegration of Ac at independent genomic loci in somatic tissue was demonstrated by isolation of new element-flanking regions by AIMS-PCR (amplification of insertion-mutagenized sites). In addition, transmission of transposed Ac elements to progeny plants was confirmed. The results indicate that the introduced Ac element is able to transpose in barley. This is a first step towards the establishment of a transposon tagging system in this economically important crop.

A reporter gene under the control of tms or aux promoters is differentially expressed in tobacco and barley protoplasts.

Agrobacterium tumefaciens and some Agrobacterium rhizogenes strains possess auxin biosynthesis genes (tms and aux genes respectively), responsible for a de novo auxin biosynthetic pathway in transformed plant cells. A comparison is presented of the potential expression of these genes in a monocotyledonous (barley) and a dicotyledonous plant (tobacco). The promoters of the genes were translationally fused to the ß-glucuronidase reporter gene and analysed in transient expression experiments. The tms and aux fusions were highly expressed in tobacco, but not in barley. However, the aux enhancer active in tobacco, conferred low ß-glucuronidase expression in barley when fused to a truncated cauliflower mosaic virus 35S promoter. The results are discussed in relation to the differential responses to Agrobacterium infection in monocots and dicots.

TnpA product encoded by the transposable element En-1 of Zea mays is a DNA binding protein.

TnpA protein, the function encoded by the most abundant transcript of En-1 was expressed in Escherichia coli. DNA binding experiments with partially purified tnpA protein revealed that it binds to the subterminal repetitive region of En-1. TnpA protein recognizes a 12-bp-long sequence motif which is reiterated several times at the termini of En-1. Binding is reduced if the cytosine residues of CG dinucleotides and CNG trinucleotides within the motif are methylated. These data suggest a model in which the product of tnpA serves as a regulator of element activity.