Huifang Jiang

Ethylene inhibited aflatoxin biosynthesis is due to oxidative stress alleviation and related to glutathione redox state changes in Aspergillus flavus

The effect of 2-chloroethyl phosphoric acid (CEPA) on aflatoxin biosynthesis, the expression of aflatoxin biosynthetic genes, reactive oxygen species (ROS) formation, cellular redox status, and enzymes involved in glutathione consumption and regeneration in Aspergillus flavus was investigated. The results demonstrated that CEPA dose dependently inhibited aflatoxin B(1) production. The expression of two typical genes involved in aflatoxin biosynthesis, aflR and aflD, was reduced after CEPA treatment at 7 d. Meanwhile, CEPA significantly reduced ROS production and thiobarbituric acid reactive substances (TBARS), increased the ratio of reduced glutathione (GSH) and oxidized glutathione (GSSG) at 5, 6 and 7 d. The activities of glutathione peroxidase (GPx), glutathione reductase (GR), as well as glucose-6-phosphate dehydrogenase (G6PDH) were significantly inhibited after CEPA treatment at 5, 6 and 7 d. The present study suggested that ethylene reduced aflatoxin production is due to oxidative stress alleviation of fungal cells and is related to glutathione redox state changes.

Diversity characterization and association analysis of agronomic traits in a Chinese peanut (Arachis hypogaea L.) mini-core collection

Association mapping is a powerful approach for exploring the molecular basis of phenotypic variations in plants. A peanut (Arachis hypogaea L.) mini-core collection in China comprising 298 accessions was genotyped using 109 simple sequence repeat (SSR) markers, which identified 554 SSR alleles and phenotyped for 15 agronomic traits in three different environments, exhibiting abundant genetic and phenotypic diversity within the panel. A model-based structure analysis assigned all accessions to three groups. Most of the accessions had the relative kinship of less than 0.05, indicating that there were no or weak relationships between accessions of the mini-core collection. For 15 agronomic traits in the peanut panel, generally the Q + K model exhibited the best performance to eliminate the false associated positives compared to the Q model and the general linear model-simple model. In total, 89 SSR alleles were identified to be associated with 15 agronomic traits of three environments by the Q + K model-based association analysis. Of these, eight alleles were repeatedly detected in two or three environments, and 15 alleles were commonly detected to be associated with multiple agronomic traits. Simple sequence repeat allelic effects confirmed significant differences between different genotypes of these repeatedly detected markers. Our results demonstrate the great potential of integrating the association analysis and marker-assisted breeding by utilizing the peanut mini-core collection.

Genetic Diversity and Population Structure of the Major Peanut (Arachis hypogaea L.) Cultivars Grown in China by SSR Markers

One hundred and forty-six highly polymorphic simple sequence repeat (SSR) markers were used to assess the genetic diversity and population structure of 196 peanut (Arachis Hypogaea L.) cultivars which had been extensively planted in different regions in China. These SSR markers amplified 440 polymorphic bands with an average of 2.99, and the average gene diversity index was 0.11. Eighty-six rare alleles with a frequency of less than 1% were identified in these cultivars. The largest Fst or genetic distance was found between the cultivars that adapted to the south regions and those to the north regions in China. A neighbor-joining tree of cultivars adapted to different ecological regions was constructed based on pairwise Nei’s genetic distances, which showed a significant difference between cultivars from the south and the north regions. A model-based population structure analysis divided these peanut cultivars into five subpopulations (P1a, P1b, P2, P3a and P3b). P1a and P1b included most the cultivars from the southern provinces including Guangdong, Guangxi and Fujian. P2 population consisted of the cultivars from Hubei province and parts from Shandong and Henan. P3a and P3b had cultivars from the northern provinces including Shandong, Anhui, Henan, Hebei, Jiangsu and the Yangtze River region including Sichuan province. The cluster analysis, PCoA and PCA based on the marker genotypes, revealed five distinct clusters for the entire population that were related to their germplasm regions. The results indicated that there were obvious genetic variations between cultivars from the south and the north, and there were distinct genetic differentiation among individual cultivars from the south and the north. Taken together, these results provided a molecular basis for understanding genetic diversity of Chinese peanut cultivars.

Abundant Microsatellite Diversity and Oil Content in Wild Arachis Species

The peanut (Arachis hypogaea) is an important oil crop. Breeding for high oil content is becoming increasingly important. Wild Arachis species have been reported to harbor genes for many valuable traits that may enable the improvement of cultivated Arachis hypogaea, such as resistance to pests and disease. However, only limited information is available on variation in oil content. In the present study, a collection of 72 wild Arachis accessions representing 19 species and 3 cultivated peanut accessions were genotyped using 136 genome-wide SSR markers and phenotyped for oil content over three growing seasons. The wild Arachis accessions showed abundant diversity across the 19 species. A. duranensis exhibited the highest diversity, with a Shannon-Weaver diversity index of 0.35. A total of 129 unique alleles were detected in the species studied. A. rigonii exhibited the largest number of unique alleles (75), indicating that this species is highly differentiated. AMOVA and genetic distance analyses confirmed the genetic differentiation between the wild Arachis species. The majority of SSR alleles were detected exclusively in the wild species and not in A. hypogaea, indicating that directional selection or the hitchhiking effect has played an important role in the domestication of the cultivated peanut. The 75 accessions were grouped into three clusters based on population structure and phylogenic analysis, consistent with their taxonomic sections, species and genome types. A. villosa and A. batizocoi were grouped with A. hypogaea, suggesting the close relationship between these two diploid wild species and the cultivated peanut. Considerable phenotypic variation in oil content was observed among different sections and species. Nine alleles were identified as associated with oil content based on association analysis, of these, three alleles were associated with higher oil content but were absent in the cultivated peanut. The results demonstrated that there is great potential to increase the oil content in A. hypogaea by using the wild Arachis germplasm.

Genomic affinities of Arachis genus and interspecific hybrids were revealed by SRAP markers.

The Arachis genus is native to South America, and contains 70–80 described species assembled into nine sections. A better understanding of the level of speciation and taxonomic relationships is a prerequisite to the effective use of Arachis species in peanut breeding programs. Forty-eight genotypes representing 19 species in 6 sections were evaluated to assay the genetic variability within and among species, and 10 recombinant lines and those parents were identified with introgression of Arachis species chromosome segments into A.hypogaea genome using SRAP markers. Sixty of sixty-four SRAP primers tested were selected for DNA amplification reactions. A dendrogram and principal component analysis were constructed based on 353 SRAP polymorphic bands of the accessions. The number of scored polymorphic bands per each primer combination varied from 1 to 25 with an average of 5.9 per reaction. Estimates of genetic distance among the 48 accessions Arachis species ranged from 0.11 to 0.76. A-genome accessions 475845 (A. duranensis), and 331197 (A. villosa) were most closely associated to A.hypogaea. The first two PCAs accounted for 77.74% (62.02 and 15.72%) of the total variation observed and separated the different genomic groups. SRAPs also identified introgression of Arachis species chromosome segments into A.hypogaea. genome with 10 recombinant lines and those parents. The present results indicated that SRAPs can be used to determine the genetic relationships among species of the different sections of the genus Arachis and to identify introgression of Arachis genus chromosome segments into A.hypogaea genome.

Genome-wide analysis of the basic leucine zipper (bZIP) transcription factor gene family in six legume genomes.

BackgroundPlant bZIP proteins characteristically harbor a highly conserved bZIP domain with two structural features: a DNA-binding basic region and a leucine (Leu) zipper dimerization region. They have been shown to be diverse transcriptional regulators, playing crucial roles in plant development, physiological processes, and biotic/abiotic stress responses. Despite the availability of six completely sequenced legume genomes, a comprehensive investigation of bZIP family members in legumes has yet to be presented.ResultsIn this study, we identified 428 bZIP genes encoding 585 distinct proteins in six legumes, Glycine max, Medicago truncatula, Phaseolus vulgaris, Cicer arietinum, Cajanus cajan, and Lotus japonicus. The legume bZIP genes were categorized into 11 groups according to their phylogenetic relationships with genes from Arabidopsis. Four kinds of intron patterns (a–d) within the basic and hinge regions were defined and additional conserved motifs were identified, both presenting high group specificity and supporting the group classification. We predicted the DNA-binding patterns and the dimerization properties, based on the characteristic features in the basic and hinge regions and the Leu zipper, respectively, which indicated that some highly conserved amino acid residues existed across each major group. The chromosome distribution and analysis for WGD-derived duplicated blocks revealed that the legume bZIP genes have expanded mainly by segmental duplication rather than tandem duplication. Expression data further revealed that the legume bZIP genes were expressed constitutively or in an organ-specific, development-dependent manner playing roles in multiple seed developmental stages and tissues. We also detected several key legume bZIP genes involved in drought- and salt-responses by comparing fold changes of expression values in drought-stressed or salt-stressed roots and leaves.ConclusionsIn summary, this genome-wide identification, characterization and expression analysis of legume bZIP genes provides valuable information for understanding the molecular functions and evolution of the legume bZIP transcription factor family, and highlights potential legume bZIP genes involved in regulating tissue development and abiotic stress responses.

Comparison of Genetic Diversity Based on SSR Markers Between Peanut Mini Core Collections from China and ICRISAT

Mini core collection plays an important role in evaluating genetic resources of peanut (Arachis hypogaea L.). This study aimed at comparing the genetic diversities of a domestic and exotic peanut mini core collections and providing basic data for germplasm introduction and peanut breeding. The exotic mini core collection, which was introduced from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT, Patancheru, India), consisted of 168 accessions, whereas the Chinese mini core collection consisted of 298 accessions. A total of 26 polymorphic simple sequence repeat (SSR) markers were used to evaluate the genetic diversity of these genotypes and their similarities. The similarity coefficient ranged from 0.49 to 0.99 among the total 466 accessions and the largest genetic distance was between “L2 Gangguo” from the Chinese core collection and “ICG12625” from the ICRISAT core collection. Among the 6 botanical types of peanut, the fastigiata type had the largest genetic diversity indices in both Chinese and ICRISAT mini core collections, which were 1.11 and 0.97, respectively. The hypogaea type had the second largest diversity with genetic diversity indices of 0.89 and 0.88 for Chinese and ICRISAT mini core collections, respectively. The genetic distance between the 2 mini core collections was larger than that within a mini core collection. Particularly, the aequatoriana genotype ICG12625 from ICRISAT had the largest differences to the Chinese genotypes. According to similarity coefficient and genetic diversity index, the genetic diversity was greater among genotypes from the Chinese mini core collection than that from the ICRISAT mini core collection

Characterization and Transferable Utility of Microsatellite Markers in the Wild and Cultivated Arachis Species.

Microsatellite or simple sequence repeat (SSR) is one of the most widely distributed molecular markers that have been widely utilized to assess genetic diversity and genetic mapping for important traits in plants. However, the understanding of microsatellite characteristics in Arachis species and the currently available amount of high-quality SSR markers remain limited. In this study, we identified 16,435 genome survey sequences SSRs (GSS-SSRs) and 40,199 expressed sequence tag SSRs (EST-SSRs) in Arachis hypogaea and its wild relative species using the publicly available sequence data. The GSS-SSRs had a density of 159.9–239.8 SSRs/Mb for wild Arachis and 1,015.8 SSR/Mb for cultivated Arachis, whereas the EST-SSRs had the density of 173.5–384.4 SSR/Mb and 250.9 SSRs/Mb for wild and cultivated Arachis, respectively. The trinucleotide SSRs were predominant across Arachis species, except that the dinucleotide accounted for most in A. hypogaea GSSs. From Arachis GSS-SSR and EST-SSR sequences, we developed 2,589 novel SSR markers that showed a high polymorphism in six diverse A. hypogaea accessions. A genetic linkage map that contained 540 novel SSR loci and 105 anchor SSR loci was constructed by case of a recombinant inbred lines F6 population. A subset of 82 randomly selected SSR markers were used to screen 39 wild and 22 cultivated Arachis accessions, which revealed a high transferability of the novel SSRs across Arachis species. Our results provided informative clues to investigate microsatellite patterns across A. hypogaea and its wild relative species and potentially facilitate the germplasm evaluation and gene mapping in Arachis species.

Identification of ERF genes in peanuts and functional analysis of AhERF008 and AhERF019 in abiotic stress response

Ethylene-responsive factor (ERF) play an important role in regulating gene expression in plant development and response to stresses. In peanuts (Arachis hypogaea L.), which produce flowers aerially and pods underground, only a few ERF genes have been identified so far. This study identifies 63 ERF unigenes from 247,313 peanut EST sequences available in the NCBI database. The phylogeny, gene structures, and putative conserved motifs in the peanut ERF proteins were analysed. Comparative analysis revealed the absence of two subgroups (A1 and A3) of the ERF family in peanuts; only 10 subgroups were identified in peanuts compared to 12 subgroups in Arabidopsis and soybeans. AP2/ERF domains were found to be conserved among peanuts, Arabidopsis, and soybeans. Outside the AP2/ERF domain, many soybean-specific conserved motifs were also detected in peanuts. The expression analysis of ERF family genes representing each clade revealed differential expression patterns in response to biotic and abiotic stresses. Overexpression of AhERF008 influenced the root gravity of Arabidopsis, whereas overexpression of AhERF019 enhanced tolerance to drought, heat, and salt stresses in Arabidopsis. The information generated in this study will be helpful to further investigate the function of ERFs in plant development and stress response.

Peanut Aflatoxin and Genomics Research in China: Progress and Perspectives

Peanut is an important oil and food crop in China with a unique role in agricultural development and food security. Aflatoxin contamination in peanut, normally more serious in southern parts of the country, is a crucial factor affecting sustainable development of the peanut industry. Extensive efforts have been made at several institutions in China for aflatoxin management and related genomics research. Several local peanut germplasm lines have been identified as resistant to seed infection by Aspergillus flavus or aflatoxin production. Two AFLP markers have been identified that are linked with resistance to seed invasion and one was converted into a SCAR marker for more efficient breeding application. Several new peanut cultivars with improved productivity and possessing resistance to aflatoxin contamination are extensively used in production. Integrated management approaches have been recommended to farmers based on agro-ecological characteristics in different regions. More recently, molecular techniques have been extensively used in genetic diversity assessment, investigation of genetic relationships among different germplasm groups, marker development, identification of interspecific genome introgression, gene cloning and function analysis, and genetic transformation of important traits concerning productivity, quality and food safety of peanut. Special emphasis has been placed on resistance to aflatoxin, bacterial wilt, foliar diseases and fatty acid desaturase. Perspectives of peanut genetic improvement and further research priorities are also discussed.