Characterization and genetics of multiple soybean aphid biotype resistance in five soybean plant introductions

Key message

Five soybean plant introductions expressed antibiosis resistance to multiple soybean aphid biotypes. Two introductions had resistance genes located in the Rag1, Rag2, and Rag3 regions; one introduction had resistance genes located in the Rag1, Rag2, and rag4 regions; one introduction had resistance genes located in the Rag1 and Rag2 regions; and one introduction had a resistance gene located in the Rag2 region.

Abstract

Soybean aphid (Aphis glycines Matsumura) is the most important soybean [Glycine max (L.) Merr.] insect pest in the USA. The objectives of this study were to characterize the resistance expressed in five plant introductions (PIs) to four soybean aphid biotypes, determine the mode of resistance inheritance, and identify markers associated with genes controlling resistance in these accessions. Five soybean PIs, from an initial set of 3000 PIs, were tested for resistance against soybean aphid biotypes 1, 2, 3, and 4 in choice and no-choice tests. Of these five PIs, PI 587663, PI 587677, and PI 587685 expressed antibiosis against all four biotypes, while PI 587972 and PI 594592 expressed antibiosis against biotypes 1, 2, and 3. F₂ populations derived from PI 587663 and PI 587972 were evaluated for resistance against soybean aphid biotype 1, and populations derived from PIs 587677, 587685, and 594592 were tested against biotype 3. In addition, F_2:3 plants were tested against biotypes 2 and 3. Genomic DNA from F₂ plants was screened with markers linked to Rag1, Rag2, Rag3, and rag4 soybean aphid-resistance genes. Results showed that PI 587663 and PI 594592 each had three genes with variable gene action located in the Rag1, Rag2, and Rag3 regions. PI 587677 had three genes with variable gene action located in the Rag1, Rag2 and rag4 regions. PI 587685 had one dominant gene located in the Rag1 region and an additive gene in the Rag2 region. PI 587972 had one dominant gene located in the Rag2 region controlling antixenosis- or antibiosis-type resistance to soybean aphid biotypes 1, 2, or 3. PIs 587663, 587677, and 587685 also showed antibiosis-type resistance against biotype 4. Information on multi-biotype aphid resistance and resistance gene markers will be useful for improving soybean aphid resistance in commercial soybean cultivars.

     

Cytochrome P<Subscript>450</Subscript>, CYP93A1, as defense marker in soybean

Cytochrome P₄₅₀, CYP93A1, is involved in the synthesis of the phytoalexin glyceollin in soybean (Glycine max L. Merr). The gene encoding CYP93A1 has been used as defense marker in soybean cell cultures, however, little is known regarding how this gene is expressed in the intact plant. To further understand the tissue-specific role of CYP93A1 in soybean defense, we analyzed the expression of this gene in mechanically damaged leaves and stems. In leaves, CYP93A1 was constitutively expressed; its expression did not change in response to mechanical damage. In stems, however, expression of CYP93A1 was induced as quickly as 4 h after mechanical damage and remained upregulated for at least 48 h. The induction of CYP93A1 was associated with the synthesis of glyceollins. In comparison to several other defense-related genes encoding cysteine protease inhibitors L1 and R1 and storage proteins vspA and vspB, CYP93A1 was the most strongly induced by stem wounding. The induction of CYP93A1 was observed only locally, not systemically. Similar stem expression patterns were consistently observed among three different soybean genotypes. The strong induction of CYP93A1 in mechanically damaged stems suggests an important role in the soybean stem defense response; therefore, this study expands the use of CYP93A1 as a defense response marker to stems, not just soybean cell cultures.     

A betaine aldehyde dehydrogenase gene from <Emphasis Type="Italic">Ammopiptanthus nanus</Emphasis> enhances tolerance of <Emphasis Type="Italic">Arabidopsis</Emphasis> to high salt and drought stresses

YUCCA is an important enzyme which catalyzes a key rate-limiting step in the tryptophan-dependent pathway for auxin biosynthesis and implicated in several processes during plant growth and development. Genome wide analyses of YUCCA genes have been performed in Arabidopsis, rice, tomato, and Populus, but have never been characterized in soybean, one of the most important oil crops in the world. In this study, 22 GmYUCCA genes (GmYUCCA1-22) were identified and named based on soybean whole-genome sequence. Phylogenetic analysis of YUCCA proteins from Glycine max, Arabidopsis, Oryza sativa, tomato, and Populus euphratica revealed that GmYUCCA proteins could be divided into four subfamilies. Quantitative real-time RT-PCR (qRT-PCR) analysis showed that GmYUCCA genes have diverse expression patterns in different tissues and under various stress treatments. Compared to the wild type (WT), the transgenic GmYUCCA5 Arabidopsis plants displayed downward curling of the leaf blade margin, evident apical dominance, higher plant height, and shorter length of siliques. Our results provide a comprehensive analysis of the soybean YUCCA gene family and lay a solid foundation for further experiments in order to functionally characterize these gene members during soybean growth and development.     

Genome-wide analysis of the PHB gene family in <Emphasis Type="Italic">Glycine max</Emphasis> (L.) Merr.

Prohibitins (PHBs) have one SPFH domain in common and present in species ranging from prokaryotes to eukaryotes. Although a number of researches on PHBs were performed in different plant species, a systematic analysis of the PHB family in soybean is still remains uncharacterized. In the present study, 24 putative PHB genes have been first systemically identified in soybean. According to phylogenetic analysis, these GmPHBs could be classified into four groups. Gene structures and motif patterns showed high levels of conservation within the phylogenetic subgroups. Several members of this family have undergone purifying selection based on Ka/Ks analysis on duplicated PHB genes in soybean. We performed microsynteny analysis across four legume species based on the comparisons among the specific regions contained in PHB genes. As a result, numerous microsyntenic gene pairs among soybean, Medicago, Lotus and Phaseolus were identified. Most soybean PHB genes exhibited different expression levels in various tissues and developmental stages through expression analysis using publicly available RNA-seq datasets. The 11 GmPHB genes from III_B subgroup were examined by qPCR for their expression in two soybean cultivar after infection by Phytophthora sojae. Besides three GmPHB genes previous reported by us, here other four genes also were rapidly induced by P. sojae infection in the resistant genotype, while induction was very weak in the susceptible genotype. The comprehensive overview of the PHB gene family in soybean genome will provide useful information for further functional analysis of the PHB gene family in soybean.     

Molecular Elucidation of Two Novel Seed Specific Flavonoid Glycosyltransferases in Soybean

Flavonoids are specialized plant secondary metabolites that are mainly present as glycoconjugates and function as attractants to pollinators and symbionts, UV protectants, allelochemicals, and have antimicrobial and antiherbivore activity for plant health. Because of the heterogeneity of UDP-glycosyltransferases (UGTs) for glycosylation in plants, their function in flavonoid glycosylation remains largely unknown in soybean and other legumes, particularly that of the UGT92 genes. Here, we identified 152 putative UGT92 genes across 48 plant species and elucidated their mode of duplication, expansion/deletion pattern, alignment, phylogenetic analysis, and genome-wide distribution. Two novel UGT-encoding genes Glyma14g04790 (UGT92G1) and Glyma15g03670 (UGT92G2) were isolated from soybean and their heterologous expression was optimized in Escherichia. coli. Both genes exhibited catalytic activity toward quercetin, kaempferol, and myricetin, with UDPglucose as the sugar donor and were characterized as flavanol-specific UGTs. High expression of both UGTs was observed in adaxial and abaxial parenchyma, suspensor cells, and adaxial and abaxial epidermis cells during seed development, suggesting that they are seed-specific flavanol glycosyltransferases in soybean. Co-expression analysis of UGT92 genes with their first and second neighborhood genes provided a basis for their network elucidation in soybean. We provide valuable information on the role of UGT92 in seed development via the glycosylation of multiple flavanols and the potential metabolic engineering of flavonoid compounds in both plants and E. coli.     

Genome-wide identification and expression analysis of the GRAS family proteins in <Emphasis Type="Italic">Medicago truncatula</Emphasis>

The GRAS gene family performs a variety of functions in plant growth and development processes, and they also play essential roles in plant response to environmental stresses. Medicago truncatula is a diploid plant with a small genome used as a model organism. Despite the vital role of GRAS genes in plant growth regulation, few studies on these genes in M. truncatula have been conducted to date. Using the M. truncatula reference genome data, we identified 68 MtGRAS genes, which were classified into 16 groups by phylogenetic analysis, located on eight chromosomes. The structure analysis indicated that MtGRAS genes retained a relatively constant exon–intron composition during the evolution of the M. truncatula genome. Most of the closely related members in the phylogenetic tree had similar motif compositions. Different motifs distributed in different groups of the MtGRAS genes were the sources of their functional divergence. Twenty-eight MtGRAS genes were expressed in six tissues, namely root, bud, blade, seedpod, nodule, and flower tissues, suggesting their putative function in many aspects of plant growth and development. Nine MtGRAS genes were upregulated under cold, freezing, drought, ABA, and salt stress treatments, indicating that they play vital roles in the response to abiotic stress in M. truncatula. Our study provides valuable information that can be utilized to improve the quality and agronomic benefits of M. truncatula and other plants.