Five new binary vectors have been constructed which have the following features: (1) different plant selectable markers including neomycin phosphotransferase (nptII), hygromycin phosphotransferase (hpt), dihydrofolate reductase (dhfr), phosphinothricin acetyl transferase (bar), and bleomycin resistance (ble); (2) selectable markers are located near the T-DNA left border and; (3) selectable marker and beta-glucuronidase (uidA) reporter genes are divergently organized for efficient expression, and can easily be removed or replaced as needed.

Different patterns of T-DNA integration in Arabidopsis were obtained that depended on whether a root or a leaf-disc transformation method was used. An examination of 82 individual transgenic Arabidopsis plants, derived from 15 independent Agrobacterium-mediated transformations in which different cointegrate and binary constructs were used, indicated that the transformation method had a significant influence on the type and copy number of T-DNA integration events. Southern hybridizations showed that most of the transgenic plants produced by a leaf-disc method contained multiple T-DNA insertions (89%), the majority of which were organized as right-border inverted repeat structures (58%). In contrast, a root transformation method mostly resulted in single T-DNA insertions (64%), with fewer right-border inverted repeats (38%). The transformation vectors, including cointegrate and binary types, and the plant selectable markers, hygromycin phosphotransferase and dihydrofolate reductase, did not appear to influence the T-DNA integration patterns.

The T-region of Ti plasmids expresses two genes (No. 1 and 2) in crown-gall cells which are essential for auxin effects. It has been shown that gene 2 (=IaaH) codes for an amidohydrolase which converts indole-3-acetamide into indole-3-acetic acid and which is functional in bacteria and in crown-gall cells (Schröder et al. (1984), Eur. J. Biochem. 138, 387-391). In this report we describe a quantitative assay for the enzyme and its application to analyze the properties of the enzyme as expressed in plant cells and in Escherichia coli. The enzyme requires no cofactors, and the temperature optimum (30-37°C), pH optimum (8.5-9.5), and Km (about 1 μM) were very similar in both systems. Besides indole-3-acetamide, the enzyme also hydrolyzed indole-3-acetonitrile, esters of indole-3-acetic acid with glucose and myo-inositol, a-naphthaleneacetamide, and phenylacetamide, indicating that it may have a general function in converting substances of low auxin activity into those with high auxin activity. The results are discussed in relation to the possible function of T-DNA gene 1 which cooperates with gene 2 in evoking auxin effects in crown-gall cells.

A recessive mutant with white leaves was identified in a screen of a population of T-DNA-tagged Arabidopsis thaliana plants. The mutation is lethal, but plants develop almost to maturity under sterile conditions. The white areas in leaves are devoid of developed chloroplasts, but the plants frequently develop green sectors which contain green chloroplasts. Molecular characterisation of the affected gene revealed that the mutant is allelic to pale cress (pac), a recently described mutation, and was therefore named pac-2. Sequencing of cDNAs and the genomic region revealed several noteworthy features of this genetic locus. In pac-2 the T-DNA had inserted in the region of the promoter and abolished transcription of the PAC gene completely. Cytokinin induced greening in mature, white homozygous pac-2 plants, and therefore is likely to be responsible for the greening observed in callus and shoots induced on roots from such plants. However, the PAC transcript was found to be absent in both white leaves and green callus. Thus, since cytokinin induced greening in the absence of PAC RNA this plant hormone appears to be able to bypass PAC function.

A modified root explant transformation method has been developed that is effective in producing transgenic Arabidopsis thaliana plants which are methotrexate resistant due to the integration of T-DNA vectors containing a chimeric dihydrofolate reductase gene. Molecular analysis shows that transformed methotrexate resistant plants contain the expected T-DNA construct with the chimeric gene. This transformation method also works well with other plant selectable markers, including hygromycin phosphotransferase and neomycin phosphotransferase II.