Transcriptome profiling, physiological, and biochemical analyses provide new insights towards drought stress response in sugar maple (Acer saccharum Marshall) saplings.

Sugar maple (Acer saccharum Marshall) is a temperate tree species in the northeastern parts of the United States and is economically important for its hardwood and syrup production. Sugar maple trees are highly vulnerable to changing climatic conditions, especially drought, so understanding the physiological, biochemical, and molecular responses is critical. The sugar maple saplings were subjected to drought stress for 7, 14, and 21 days and physiological data collected at 7, 14, and 21 days after stress (DAS) showed significantly reduced chlorophyll and Normalized Difference Vegetation Index with increasing drought stress time. The drought stress-induced biochemical changes revealed a higher accumulation of malondialdehyde, proline, and peroxidase activity in response to drought stress. Transcriptome analysis identified a total of 14,099 differentially expressed genes (DEGs); 328 were common among all stress periods. Among the DEGs, transcription factors (including NAC, HSF, ZFPs, GRFs, and ERF), chloroplast-related and stress-responsive genes such as peroxidases, membrane transporters, kinases, and protein detoxifiers were predominant. GO enrichment and KEGG pathway analysis revealed significantly enriched processes related to protein phosphorylation, transmembrane transport, nucleic acids, and metabolic, secondary metabolite biosynthesis pathways, circadian rhythm-plant, and carotenoid biosynthesis in response to drought stress. Time-series transcriptomic analysis revealed changes in gene regulation patterns in eight different clusters, and pathway analysis by individual clusters revealed a hub of stress-responsive pathways. In addition, qRT-PCR validation of selected DEGs revealed that the expression patterns were consistent with transcriptome analysis. The results from this study provide insights into the dynamics of physiological, biochemical, and gene responses to progressive drought stress and reveal the important stress-adaptive mechanisms of sugar maple saplings in response to drought stress.

Genomic and evolutionary relationships among wild and cultivated blueberry species.

BACKGROUND: Blueberries (Vaccinium section Cyanococcus) are an economically important fruit crop in the United States. Understanding genetic structure and relationships in blueberries is essential to advance the genetic improvement of horticulturally important traits. In the present study, we investigated the genomic and evolutionary relationships in 195 blueberry accessions from five species (comprising 33 V. corymbosum, 14 V. boreale, 81 V. darrowii, 29 V. myrsinites, and 38 V. tenellum) using single nucleotide polymorphisms (SNPs) mined from genotyping-by-sequencing (GBS) data. RESULTS: GBS generated ~ 751 million raw reads, of which 79.7% were mapped to the reference genome V. corymbosum cv. Draper v1.0. After filtering (read depth > 3, minor allele frequency > 0.05, and call rate > 0.9), 60,518 SNPs were identified and used in further analyses. The 195 blueberry accessions formed three major clusters on the principal component (PC) analysis plot, in which the first two PCs accounted for 29.2% of the total genetic variance. Nucleotide diversity (π) was highest for V. tenellum and V. boreale (0.023 each), and lowest for V. darrowii (0.012). Using TreeMix analysis, we identified four migration events and deciphered gene flow among the selected species. In addition, we detected a strong V. boreale lineage in cultivated blueberry species. Pairwise SweeD analysis identified a wide sweep (encompassing 32 genes) as a strong signature of domestication on the scaffold VaccDscaff 12. From this region, five genes encoded topoisomerases, six genes encoded CAP-gly domain linker (which regulates the dynamics of the microtubule cytoskeleton), and three genes coded for GSL8 (involved in the synthesis of the cell wall component callose). One of the genes, augustus_masked-VaccDscaff12-processed-gene-172.10, is a homolog of Arabidopsis AT2G25010 and encodes the protein MAINTENANCE OF MERISTEMS-like involved in root and shoot growth. Additional genomic stratification by admixture analysis identified genetic lineages and species boundaries in blueberry accessions. The results from this study indicate that V. boreale is a genetically distant outgroup, while V. darrowii, V. myrsinites, and V. tenellum are closely related. CONCLUSION: Our study provides new insights into the evolution and genetic architecture of cultivated blueberries.

Differential Morpho-Physiological and Transcriptomic Responses to Heat Stress in Two Blueberry Species.

Blueberries (Vaccinium spp.) are highly vulnerable to changing climatic conditions, especially increasing temperatures. To gain insight into mechanisms underpinning the response to heat stress, two blueberry species were subjected to heat stress for 6 and 9 h at 45 °C, and leaf samples were used to study the morpho-physiological and transcriptomic changes. As compared with Vaccinium corymbosum, Vaccinium darrowii exhibited thermal stress adaptation features such as small leaf size, parallel leaf orientation, waxy leaf coating, increased stomatal surface area, and stomatal closure. RNAseq analysis yielded ~135 million reads and identified 8305 differentially expressed genes (DEGs) during heat stress against the control samples. In V. corymbosum, 2861 and 4565 genes were differentially expressed at 6 and 9 h of heat stress, whereas in V. darrowii, 2516 and 3072 DEGs were differentially expressed at 6 and 9 h, respectively. Among the pathways, the protein processing in the endoplasmic reticulum (ER) was the highly enriched pathway in both the species: however, certain metabolic, fatty acid, photosynthesis-related, peroxisomal, and circadian rhythm pathways were enriched differently among the species. KEGG enrichment analysis of the DEGs revealed important biosynthesis and metabolic pathways crucial in response to heat stress. The GO terms enriched in both the species under heat stress were similar, but more DEGs were enriched for GO terms in V. darrowii than the V. corymbosum. Together, these results elucidate the differential response of morpho-physiological and molecular mechanisms used by both the blueberry species under heat stress, and help in understanding the complex mechanisms involved in heat stress tolerance.

An Integrated Approach of QTL Mapping and Genome-Wide Association Analysis Identifies Candidate Genes for Phytophthora Blight Resistance in Sesame (Sesamum indicum L.).

Phytophthora blight (PB) caused by Phytophthora nicotianae is a highly destructive disease in sesame (Sesamum indicum L.). In this study, we used linkage mapping and genome-wide association study (GWAS) to identify quantitative trait loci (QTL) and candidate genes associated with PB resistance. The QTL mapping in 90 RILs of the Goenbaek × Osan cross using genotyping-by-sequencing detected significant QTLs for PB resistance on chromosome 10, explaining 12.79%-13.34% of phenotypic variation. Association of this locus to PB resistance was also revealed through bulked segregant analysis in second RIL population (Goenbaek × Milsung cross) comprising 188 RILs. The GWAS of 87 sesame accessions evaluated against three P. nicotianae isolates identified 29 SNPs on chromosome 10 significantly associated with PB resistance. These SNPs were located within a 0.79 Mb region, which co-located with the QTL intervals identified in RIL populations, and hence scanned for identifying candidate genes. This region contained several defense-related candidate R genes, five of which were selected for quantitative expression analysis. One of these genes, SIN_1019016 was found to show significantly higher expression in the resistant parent compared to that in the susceptible parents and selected RILs. Paired-end sequencing of the gene SIN_1019016 in parental cultivars revealed two synonymous SNPs between Goenbaek and Osan in exon 2 of coding DNA sequence. These results suggested SIN_1019016 as one of the candidate gene conferring PB resistance in sesame. The findings from this study will be useful in the marker-assisted selection as well as the functional analysis of PB resistance candidate gene(s) in sesame.

Admixture Analysis Using Genotyping-by-Sequencing Reveals Genetic Relatedness and Parental Lineage Distribution in Highbush Blueberry Genotypes and Cross Derivatives.

Blueberries (Vaccinium section Cyanococcus) are perennial shrubs widely cultivated for their edible fruits. In this study, we performed admixture and genetic relatedness analysis of northern highbush (NHB, primarily V. corymbosum) and southern highbush (SHB, V. corymbosum introgressed with V. darrowii, V. virgatum, or V. tenellum) blueberry genotypes, and progenies of the BNJ16-5 cross (V. corymbosum × V. darrowii). Using genotyping-by-sequencing (GBS), we generated more than 334 million reads (75 bp). The GBS reads were aligned to the V. corymbosum cv. Draper v1.0 reference genome sequence, and ~2.8 million reads were successfully mapped. From the alignments, we identified 2,244,039 single-nucleotide polymorphisms, which were used for principal component, haplotype, and admixture analysis. Principal component analysis revealed three main groups: (1) NHB cultivars, (2) SHB cultivars, and (3) BNJ16-5 progenies. The overall fixation index (FST) and nucleotide diversity for NHB and SHB cultivars indicated wide genetic differentiation, and haplotype analysis revealed that SHB cultivars are more genetically diverse than NHB cultivars. The admixture analysis identified a mixture of various lineages of parental genomic introgression. This study demonstrated the effectiveness of GBS-derived single-nucleotide polymorphism markers in genetic and admixture analyses to reveal genetic relatedness and to examine parental lineages in blueberry, which may be useful for future breeding plans.

Insight Into the Prospects for the Improvement of Seed Starch in Legume-A Review.

In addition to proteins and/or oils, mature seeds of most legume crops contain important carbohydrate components, including starches and sugars. Starch is also an essential nutritional component of human and animal diets and has various food and non-food industrial applications. Starch is a primary insoluble polymeric carbohydrate produced by higher plants and consists of amylose and amylopectin as a major fraction. Legume seeds are an affordable source of not only protein but also the starch, which has an advantage of being resistant starch compared with cereal, root, and tuber starch. For these reasons, legume seeds form a good source of resistant starch-rich healthy food with a high protein content and can be utilized in various food applications. The genetics and molecular details of starch and other carbohydrate components are well studied in cereal crops but have received little attention in legumes. In order to improve legume starch content, quality, and quantity, it is necessary to understand the genetic and molecular factors regulating carbohydrate metabolism in legume crops. In this review, we assessed the current literature reporting the genetic and molecular basis of legume carbohydrate components, primarily focused on seed starch content. We provided an overview of starch biosynthesis in the heterotrophic organs, the chemical composition of major consumable legumes, the factors influencing starch digestibility, and advances in the genetic, transcriptomic, and metabolomic studies in important legume crops. Further, we discussed breeding and biotechnological approaches for the improvement of the starch composition in major legume crops. The information reviewed in this study will be helpful in facilitating the food and non-food applications of legume starch and provide economic benefits to farmers and industries.

Harnessing the Potential of Forage Legumes, Alfalfa, Soybean, and Cowpea for Sustainable Agriculture and Global Food Security.

Substantial improvements in access to food and increased purchasing power are driving many people toward consuming nutrition-rich foods causing an unprecedented demand for protein food worldwide, which is expected to rise further. Forage legumes form an important source of feed for livestock and have potential to provide a sustainable solution for food and protein security. Currently, alfalfa is a commercially grown source of forage and feed in many countries. However, soybean and cowpea also have the potential to provide quality forage and fodder for animal use. The cultivation of forage legumes is under threat from changing climatic conditions, indicating the need for breeding cultivars that can sustain and acclimatize to the negative effects of climate change. Recent progress in genetic and genomic tools have facilitated the identification of quantitative trait loci and genes/alleles that can aid in developing forage cultivars through genomics-assisted breeding. Furthermore, transgenic technology can be utilized to manipulate the genetic makeup of plants to improve forage digestibility for better animal performance. In this article, we assess the genetic potential of three important legume crops, alfalfa, soybean, and cowpea in supplying quality fodder and feed for livestock. In addition, we examine the impact of climate change on forage quality and discuss efforts made in enhancing the adaptation of the plant to the abiotic stress conditions. Subsequently, we suggest the application of integrative approaches to achieve adequate forage production amid the unpredictable climatic conditions.

Comparative genome analysis to identify SNPs associated with high oleic acid and elevated protein content in soybean.

The objective of this study was to determine the genetic relationship between the oleic acid and protein content. The genotypes having high oleic acid and elevated protein (HOEP) content were crossed with five elite lines having normal oleic acid and average protein (NOAP) content. The selected accessions were grown at six environments in three different locations and phenotyped for protein, oil, and fatty acid components. The mean protein content of parents, HOEP, and NOAP lines was 34.6%, 38%, and 34.9%, respectively. The oleic acid concentration of parents, HOEP, and NOAP lines was 21.7%, 80.5%, and 20.8%, respectively. The HOEP plants carried both FAD2-1A (S117N) and FAD2-1B (P137R) mutant alleles contributing to the high oleic acid phenotype. Comparative genome analysis using whole-genome resequencing data identified six genes having single nucleotide polymorphism (SNP) significantly associated with the traits analyzed. A single SNP in the putative gene Glyma.10G275800 was associated with the elevated protein content, and palmitic, oleic, and linoleic acids. The genes from the marker intervals of previously identified QTL did not carry SNPs associated with protein content and fatty acid composition in the lines used in this study, indicating that all the genes except Glyma.10G278000 may be the new genes associated with the respective traits.

A substitution mutation in OsCCD7 cosegregates with dwarf and increased tillering phenotype in rice.

Dwarf plant height and tillering ability are two of the most important agronomic traits that determine the plant architecture, and have profound influence on grain yield in rice. To understand the molecular mechanism controlling these two traits, an EMS-induced recessive dwarf and increased tillering1 (dit1) mutant was characterized. The mutant showed proportionate reduction in each internode as compared to wild type revealing that it belonged to the category of dn-type of dwarf mutants. Besides, exogenous application of GA3 and 24-epibrassinolide, did not have any effect on the phenotype of the mutant. The gene was mapped on the long arm of chromosome 4, identified through positional candidate approach and verified by cosegregation analysis. It was found to encode carotenoid cleavage dioxygenase7 (CCD7) and identified as an allele of htd1. The mutant carried substitution of two nucleotides CC to AA in the sixth exon of the gene that resulted in substitution of serine by a stop codon in the mutant, and thus formation of a truncated protein, unlike amino acid substitution event in htd1. The new allele will facilitate further functional characterization of this gene, which may lead to unfolding of newer signalling pathways involving plant development and architecture.