No abstract

Soybean cyst nematode (SCN) is the most devastating pathogen of soybean. Information about the molecular basis of soybean-SCN interactions is needed to assist future development of effective management tools against this pathogen. Toward this end, soybean transcript abundance was measured using the Affymetrix Soybean Genome Array in a susceptible and a resistant reaction of soybean to SCN infection. Two genetically related soybean sister lines TN02-226 and TN02-275, which are resistant and susceptible, respectively, to the SCN race 2 infection were utilized in these experiments. Pairwise comparisons followed by false discovery rate analysis indicated that the expression levels of 162 transcripts changed significantly in the resistant line, of which 84 increased while 78 decreased. However, in the susceptible line, 1,694 transcripts changed significantly, of which 674 increased while 1,020 decreased. Comparative analyses of these transcripts indicated that a total of 51 transcripts were in common between resistance and susceptible responses. In this set, 42 transcripts increased in the resistant line, but decreased in the susceptible line. Quantitative real-time reverse-transcription polymerase chain reaction confirmed the results of microarray analysis. Of the transcripts to which a function could be assigned, genes were associated with metabolism, cell wall modification, signal transduction, transcription, and defense. Microarray analyses examining two genetically related soybean lines against the same SCN population provided additional insights into the specific changes in gene expression of a susceptible and a resistant reaction beneficial for identification of genes involved in defense.

Some transgenic crops can introgress genes into other varieties of the crop, to related weeds or themselves remain as 'volunteer' weeds, potentially enhancing the invasiveness or weediness of the resulting offspring. The presently suggested mechanisms for transgene containment allow low frequency of gene release (leakage), requiring the mitigation of continued spread. Transgenic mitigation (TM), where a desired primary gene is tandemly coupled with mitigating genes that are positive or neutral to the crop but deleterious to hybrids and their progeny, was tested as a mechanism to mitigate transgene introgression. Dwarfism, which typically increases crop yield while decreasing the ability to compete, was used as a mitigator. A construct of a dominant ahasR (acetohydroxy acid synthase) gene conferring herbicide resistance in tandem with the semidominant mitigator dwarfing Delta gai (gibberellic acid-insensitive) gene was transformed into tobacco (Nicotiana tabacum). The integration and the phenotypic stability of the tandemly linked ahasR and Delta gai genomic inserts in later generations were confirmed by polymerase chain reaction. The hemizygous semidwarf imazapyr-resistant TM T1 (= BC1) transgenic plants were weak competitors when cocultivated with wild type segregants under greenhouse conditions and without using the herbicide. The competition was most intense at close spacings typical of weed offspring. Most dwarf plants interspersed with wild type died at 1-cm, > 70% at 2.5-cm and 45% at 5-cm spacing, and the dwarf survivors formed no flowers. At 10-cm spacing, where few TM plants died, only those TM plants growing at the periphery of the large cultivation containers formed flowers, after the wild type plants terminated growth. The highest reproductive TM fitness relative to the wild type was 17%. The results demonstrate the suppression of crop-weed hybrids when competing with wild type weeds, or such crops as volunteer weeds, in seasons when the selector (herbicide) is not used. The linked unfitness would be continuously manifested in future generations, keeping the transgene at a low frequency.