Genetic mapping identifies loci that influence tomato resistance against Colorado potato beetles

"The Colorado potato beetle (CPB; Leptinotarsa decemlineata Say), the most economically important insect pest on potato (Solanum tuberosum L.), also feeds on other Solanaceae, including cultivated tomato (Solanum lycopersicum L.). We used tomato genetic mapping populations to investigate natural variation in CPB resistance. CPB bioassays with 74 tomato lines carrying introgressions of Solanum pennellii in S. lycopersicum cv. M82 identified introgressions from S. pennellii on chromosomes 1 and 6 conferring CPB susceptibility, whereas introgressions on chromosomes 1, 8 and 10 conferred higher resistance. Mapping of CPB resistance using 113 recombinant inbred lines derived from a cross between S. lycopersicum cv UC-204B and Solanum galapagense identified significant quantitative trait loci on chromosomes 6 and 8. In each case, the S. galapagense alleles were associated with lower leaf damage and reduced larval growth. Results of both genetic mapping approaches converged on the same region of chromosome 6, which may have important functions in tomato defense against CPB herbivory. Although genetic mapping identified quantitative trait loci encompassing known genes for tomato acyl sugar and glycoalkaloid biosynthesis, experiments with acyl sugar near-isogenic lines and transgenic GAME9 glycoalkaloid-deficient and overproducing lines showed no significant effect of these otherwise insect-defensive metabolites on CPB performance.

Effect of defoliation on grain amaranth growth and yield in green house.

<p>Plants from different cultivars (<i>Tarasca, Dorada Amaranteca,n utrisol, Revancha</i> and <i>Gabriela</i> ) were grown equally in the green house and at panicle emergence were subjected to 2 defoliation treatments: control (0%) and 100% defoliation. Phenological parameters were measured at physiological maturity: A plant height; B shoot dry weight; C seed yield and D harvest index. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for the Dunnett test.</p

Seed composition in defoliated amaranth in green house.

<p>At mature amaranth seeds were collected and analyzed for A 100 seeds weight, B seed starch, C seed lipids and D seed protein. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for t Test.</p

Carbohydrate levels in the roots of defoliated and undamaged amaranth plants.

<p>Plants were harvested at 1, 30 and 110 days after treatment. A glucose, B fructose, C sucrose and D starch. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for Dunnett Test.</p

Sucrolytic and amylolytic activity in defoliated and shaded amaranth plants 1 day after treatment.

<p>Invertase activity in A leaf, B stem, C Root. D SUS activity in root and stem. E total amylase activity in stem and root. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for Dunnett Test.</p

Transcriptomic analysis of grain amaranth (<it>Amaranthus hypochondriacus</it>) using 454 pyrosequencing: comparison with <it>A. tuberculatus</it>, expression profiling in stems and in response to biotic and abiotic stress

<p>Abstract</p> <p>Background</p> <p><it>Amaranthus hypochondriacus</it>, a grain amaranth, is a C4 plant noted by its ability to tolerate stressful conditions and produce highly nutritious seeds. These possess an optimal amino acid balance and constitute a rich source of health-promoting peptides. Although several recent studies, mostly involving subtractive hybridization strategies, have contributed to increase the relatively low number of grain amaranth expressed sequence tags (ESTs), transcriptomic information of this species remains limited, particularly regarding tissue-specific and biotic stress-related genes. Thus, a large scale transcriptome analysis was performed to generate stem- and (a)biotic stress-responsive gene expression profiles in grain amaranth.</p> <p>Results</p> <p>A total of 2,700,168 raw reads were obtained from six 454 pyrosequencing runs, which were assembled into 21,207 high quality sequences (20,408 isotigs + 799 contigs). The average sequence length was 1,064 bp and 930 bp for isotigs and contigs, respectively. Only 5,113 singletons were recovered after quality control. Contigs/isotigs were further incorporated into 15,667 isogroups. All unique sequences were queried against the nr, TAIR, UniRef100, UniRef50 and Amaranthaceae EST databases for annotation. Functional GO annotation was performed with all contigs/isotigs that produced significant hits with the TAIR database. Only 8,260 sequences were found to be homologous when the transcriptomes of <it>A. tuberculatus </it>and <it>A. hypochondriacus </it>were compared, most of which were associated with basic house-keeping processes. Digital expression analysis identified 1,971 differentially expressed genes in response to at least one of four stress treatments tested. These included several multiple-stress-inducible genes that could represent potential candidates for use in the engineering of stress-resistant plants. The transcriptomic data generated from pigmented stems shared similarity with findings reported in developing stems of Arabidopsis and black cottonwood (<it>Populus trichocarpa</it>).</p> <p>Conclusions</p> <p>This study represents the first large-scale transcriptomic analysis of <it>A. hypochondriacus</it>, considered to be a highly nutritious and stress-tolerant crop. Numerous genes were found to be induced in response to (a)biotic stress, many of which could further the understanding of the mechanisms that contribute to multiple stress-resistance in plants, a trait that has potential biotechnological applications in agriculture.</p