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SummaryHigher plants assimilate nitrogen in the form of ammonia through the concerted activity of glutamine synthetase (GS) and glutamate synthase (GOGAT). The GS enzyme is either located in the cytoplasm (GS 1 ) or in the chloroplast (GS 2 ). Glutamine synthetase 1 is regulated in different plants at the transcriptional level and there are some reports of regulation at the level of protein stability. Here we present data that clearly establish that GS 1 in plants is also regulated at the level of transcript turnover and at the translational level. Using a Glycine max (soybean) GS 1 transgene, with and without its 3¢ untranslated region (UTR), driven by the constitutive CaMV 35S promoter in Medicago sativa (alfalfa) and Nicotiana tabacum (tobacco), we show that the 3¢ UTR plays a major role in both transcript turnover and translation repression in both the leaves and the nodules. Our data suggest that the 3¢ UTR mediated turnover of the transcript is regulated by a nitrogen metabolite or carbon/nitrogen ratios. We also show that the 3¢ UTR of the gene for the soybean GS 1 confers post-transcriptional regulation on a reporter gene. Our dissection of post-transcriptional and translational levels of regulation of GS in plants shows that the situation in plants strongly resembles that in other organisms where GS is regulated at almost all levels. Multistep regulation of GS shows the high priority given by organisms to regulating and ensuring optimal control of nitrogen substrates and preventing overproduction of glutamine and drainage of the glutamate pool.

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Degenerate primers designed from conserved motifs of known plant resistance gene products were used to amplify genomic DNA sequences from the root-knot nematode (Meloidogyne incognita) resistance genetic source, Upland cotton (Gossypium hirsutum) cultivar Auburn 634 RNR. A total of 165 clones were isolated, and sequence analysis revealed 57 of the clones to be novel nucleotide sequences, many containing the resistance (R)-protein nucleotide-binding site motif. A cluster analysis was performed with resistance gene analogue (RGA) nucleotide sequences isolated in this study, in addition to 99 cotton RGA nucleotide sequences already deposited in GenBank, to generate a phylogenetic tree of cotton R genes. The cotton RGA nucleotide sequences were arranged into 11 groups and 56 sub-groups, based on genetic distances. Multiple sequence alignments were performed on the RGA sequences of each sub-group, and either the consensus sequences or individual RGA sequences were used to design 61 RGA-sequence-tagged site primers. A recombinant inbred line (RIL) population of cultivated tetraploid cotton was genotyped using RGA-specific primers that amplified polymorphic fragments between the two RIL parents. Nine RGA markers were mapped to homeologous chromosomes 12 and 26, based on linkage to existing markers that are located on these chromosomes.

The southern root‐knot nematode (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood] is one of the most destructive pests in the Cotton Belt of the USA. The lack of an economical evaluation method for RKN resistance has hindered the development of resistant cultivars. This investigation was conducted to develop an improved RKN evaluation technique. Twelve genotypes including seven susceptible (S) lines, one moderately resistant (MR) line, three highly resistant (R) lines derived from ‘Auburn 623 RNR,’ and one F1 between DP 33B (S) and ‘Auburn 634 RNR’ (R) were evaluated in the greenhouse for plant growth, RKN egg reproduction, and root galling in Experiment 1. RKN egg reproduction was highly and positively correlated with galling index and both were highly and negatively correlated with plant growth characteristics including plant height, number of leaves, plant and root weight. Galling index was confirmed to be highly significantly and negatively correlated with plant height and fresh weight in Experiment 2 with 9 parents and their 36 F1 hybrids. Galling index had highest genotypic F value and comparable coefficient of variance (CV) to the plant characteristics, while CV for egg counts was very high. Correlation between the two greenhouse tests in the 9 parental lines as measured by galling index was highly significant. Comparison between F1 and their parents in egg reproduction and galling revealed that the RKN resistance is partially dominant. Using a common check and double inoculation in each pot, galling index is an easy, quick and reliable method for screening large numbers of cotton plants.