No abstract

The inducibility of the glucosinolate resistance mechanism is an energy-saving strategy for plants, but whether induction would still be triggered by glucosinolate-tolerant Plutella xylostella (diamondback moth, DBM) after a plant had evolved a new resistance mechanism (e.g., saponins in Barbara vulgaris) was unknown. In B. vulgaris, aromatic glucosinolates derived from homo-phenylalanine are the dominant glucosinolates, but their biosynthesis pathway was unclear. In this study, we used G-type (pest-resistant) and P-type (pest-susceptible) B. vulgaris to compare glucosinolate levels and the expression profiles of their biosynthesis genes before and after infestation by DBM larvae. Two different stereoisomers of hydroxylated aromatic glucosinolates are dominant in G- and P-type B. vulgaris, respectively, and are induced by DBM. The transcripts of genes in the glucosinolate biosynthesis pathway and their corresponding transcription factors were identified from an Illumina dataset of G- and P-type B. vulgaris. Many genes involved or potentially involved in glucosinolate biosynthesis were induced in both plant types. The expression patterns of six DBM induced genes were validated by quantitative PCR (qPCR), while six long-fragment genes were validated by molecular cloning. The core structure biosynthetic genes showed high sequence similarities between the two genotypes. In contrast, the sequence identity of two apparent side chain modification genes, the SHO gene in the G-type and the RHO in P-type plants, showed only 77.50% identity in coding DNA sequences and 65.48% identity in deduced amino acid sequences. The homology to GS-OH in Arabidopsis, DBM induction of the transcript and a series of qPCR and glucosinolate analyses of G-type, P-type and F1 plants indicated that these genes control the production of S and R isomers of 2-hydroxy-2-phenylethyl glucosinolate. These glucosinolates were significantly induced by P. xylostella larvae in both the susceptiple P-type and the resistant G-type, even though saponins are the main DBM-resistance causing metabolites in G-type plants. Indol-3-ylmethylglucosinolate was induced in the G-type only. These data will aid our understanding of the biosynthesis and induction of aromatic glucosinolates at the molecular level and also increase our knowledge of the complex mechanisms underpinning defense induction in plants.

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Brassica oleracea and B. rapa are two important vegetable crops. Both are composed of dozens of subspecies encompassing hundreds of varieties and cultivars. Synthetic B. napus with these two plants has been used extensively as a research model for the investigation of allopolyploid evolution. However, the mechanism underlying the explosive evolution of hundreds of varieties of B. oleracea and B. rapa within a short period is poorly understood. In the present study, interspecific hybridization between B. oleracea var. alboglabra and B. rapa var. purpurea was performed. The backcross progeny displayed extensive morphological variation, including some individuals that phenocopied subspecies other than their progenitors. Numerous interesting novel phenotypes and mutants were identified among the backcross progeny. The chromosomal recombination between the A and C genomes and the chromosomal asymmetric segregation were revealed using Simple Sequence Repeats (SSR) markers. These findings provide direct evidence in support of the hypothesis that interspecific hybridization and backcrossing have played roles in the evolution of the vast variety of vegetables among these species and suggest that combination of interspecific hybridization and backcrossing may facilitate the development of new mutants and novel phenotypes for both basic research and the breeding of new vegetable crops.

Effect of elevated CO 2 on feeding behavior of the cotton aphid, Aphis gossypii (Glover) (Hemiptera: Aphididae), was investigated using electrical penetration graphs (EPG) on cotton, Gossypium hirsutum L. (Malvaceae). Leaf microstructures and foliar soluble constituents were also measured simultaneously to quantify the impact of foliar changes on leaf nutritional quantity and quality, owing to elevated CO 2 , on stylet penetration and food-quality plasticity of A. gossypii. Significant increases in fresh body weight, fecundity, and population abundances of A. gossypii were found in elevated CO 2 in contrast to ambient CO 2 . Elevated CO 2 influenced the feeding behavior, as evidenced by altered EPG recordings, including the increased non-penetration period (walking and finding the feeding site), E2 <8 min (probes with sustained ingestion of <8 min), and first E2 >8 min (first occurrence of probes with sustained ingestion of >8 min), and decreased E2 >8 min recordings. Moreover, leaf microstructures were significantly affected by CO 2 levels, with thinner upside epidermis (UPE) and thicker underside epidermis (UDE), sponge tissues (ST), and fence tissues under elevated CO 2 compared to that in ambient CO 2 . Therefore, it is expected that A. gossypii spend more time penetrating the thicker leaf UDE and ST when the host plant is exposed to elevated CO 2 . Furthermore, elevated CO 2 significantly enhanced foliar soluble matter, including soluble sugars (SS), free amino acids and fatty acids (FFA), and total soluble matter (TSM), which was congruent with significant increase or decrease in leaf turgor or osmotic potential. Increased leaf turgor and leaf soluble constituents favored ingestion in A. gossypii, resulting in increases in fresh body weight, fecundity, and population abundances under elevated CO 2 . These feeding behaviors and resulting population growth parameters are consistent with the significant positive correlations between aphid fresh body weight and foliar FFA/TSM, between A. gossypii fecundity and foliar SS of cotton plants, and between the time of E2 <8 min recordings and leaf turgor.

No abstract

Sinapis alba is an important condiment crop and can also be used as a phytoremediation plant. Though it has important economic and agronomic values, sequence data, and the genetic tools are still rare in this plant. In the present study, a de novo transcriptome based on the transcriptions of leaves, stems, and roots was assembled for S. alba for the first time. The transcriptome contains 47,972 unigenes with a mean length of 1185 nt and an N50 of 1672 nt. Among these unigenes, 46,535 (97%) unigenes were annotated by at least one of the following databases: NCBI non-redundant (Nr), Swiss-Prot, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, Gene Ontology (GO), and Clusters of Orthologous Groups of proteins (COGs). The tissue expression pattern profiles revealed that 3489, 1361, and 8482 unigenes were predominantly expressed in the leaves, stems, and roots of S. alba, respectively. Genes predominantly expressed in the leaf were enriched in photosynthesis- and carbon fixation-related pathways. Genes predominantly expressed in the stem were enriched in not only pathways related to sugar, ether lipid, and amino acid metabolisms but also plant hormone signal transduction and circadian rhythm pathways, while the root-dominant genes were enriched in pathways related to lignin and cellulose syntheses, involved in plant-pathogen interactions, and potentially responsible for heavy metal chelating, and detoxification. Based on this transcriptome, 14,727 simple sequence repeats (SSRs) were identified, and 12,830 pairs of primers were developed for 2522 SSR-containing unigenes. Additionally, the glucosinolate (GSL) and phytochelatin metabolic pathways, which give the characteristic flavor and the heavy metal tolerance of this plant, were intensively analyzed. The genes of aliphatic GSLs pathway were predominantly expressed in roots. The absence of aliphatic GSLs in leaf tissues was due to the shutdown of BCAT4, MAM1, and CYP79F1 expressions. Glutathione was extensively converted into phytochelatin in roots, but it was actively converted to the oxidized form in leaves, indicating the different mechanisms in the two tissues. This transcriptome will not only benefit basic research and molecular breeding of S. alba but also be useful for the molecular-assisted transfer of beneficial traits to other crops.

Taproot skin color is a crucial visual and nutritional quality trait of radish, and purple skin is most attractive to consumers. However, the genetic mechanism underlying this character is unknown. Herein, F2 segregating populations were constructed to investigate radish genomic regions with purple skin genes. Segregation analysis suggested that pigment presence was controlled by one dominant gene, Rsps. A bulk segregant approach coupled to whole-genome sequencing (QTL-seq) and classical linkage mapping narrowed the Rsps location to a 238.51-kb region containing 18 genes. A gene in this region, designated RsMYB1.1 (an Arabidopsis PAP1 homolog), was a likely candidate gene because semiquantitative RT-PCR and quantitative real-time PCR revealed RsMYB1.1 expression in only purple-skinned genotypes, sequence variation was found between white- and purple-skinned radishes, and an InDel marker in this gene correctly predicted taproot skin color. Furthermore, four RsMYB1.1 homologs (RsMYB1.1-1.4) were found in “XYB36-2” radish. RsMYB1.1 and the previously mapped and cloned RsMYB1.4 (contributing to red skin) were located on different chromosomes and in different subclades of a phylogenetic tree; thus, they are different genes. These findings provide insight into the complex anthocyanin biosynthesis regulation in radish and information for molecular breeding to improve the anthocyanin content and appearance of radish taproots.