Determination Of Evolutionary History Of Big Bluestem Populations Through Chloroplast DNA Analysis

Andropogon gerardii Vitman (big bluestem) is one of the most dominant and widely distributed grasses of the North American prairie. It is widely used in restoration projects for the recovery of grassland ecosystems. A. gerardii demonstrates genetic and adaptive variation among populations across the prairie. With the objective to understand the evolutionary relationship between the A. gerardii populations, two noncoding chloroplast DNA (cpDNA) spacers (rpl32-trnL(UAG) and trnQ(UUG)-rps16) were studied. Similarly, genetic differentiation among the populations was also calculated based on the spacers. The trnQ(UUG)-rps16 spacer had more polymorphic sites than the rpl32-trnL(UAG) spacer. A phylogenetic tree based on combined cpDNA spacers generated a monophyletic tree for A. gerardii with a Colorado population and sand bluestem (Andropogon hallii) as the outgroups. The monophyletic tree was further resolved into two sub-clades. Most of the branches and nodes were well supported, with more than 70% of posterior probability values. However, the grouping of populations did not support the resolution of the phylogenetic tree with geological distribution. Analysis of molecular variance suggests there is a low level of genetic differentiation among the populations, with 90% of variation within the populations and 10% of variation among the populations. The observed high genetic variation within populations could be the result of potential gene flow, polyploidy, and the outcrossing nature of big bluestem

Redox-engineering enhances maize thermotolerance and grain yield in the field

Contains fulltext : 252904.pdf (Publisher’s version ) (Open Access)08 juli 202

Chromosome-level genome assembly of a regenerable maize inbred line A188.

BACKGROUND The maize inbred line A188 is an attractive model for elucidation of gene function and improvement due to its high embryogenic capacity and many contrasting traits to the first maize reference genome, B73, and other elite lines. The lack of a genome assembly of A188 limits its use as a model for functional studies. RESULTS Here, we present a chromosome-level genome assembly of A188 using long reads and optical maps. Comparison of A188 with B73 using both whole-genome alignments and read depths from sequencing reads identify approximately 1.1 Gb of syntenic sequences as well as extensive structural variation, including a 1.8-Mb duplication containing the Gametophyte factor1 locus for unilateral cross-incompatibility, and six inversions of 0.7 Mb or greater. Increased copy number of carotenoid cleavage dioxygenase 1 (ccd1) in A188 is associated with elevated expression during seed development. High ccd1 expression in seeds together with low expression of yellow endosperm 1 (y1) reduces carotenoid accumulation, accounting for the white seed phenotype of A188. Furthermore, transcriptome and epigenome analyses reveal enhanced expression of defense pathways and altered DNA methylation patterns of the embryonic callus. CONCLUSIONS The A188 genome assembly provides a high-resolution sequence for a complex genome species and a foundational resource for analyses of genome variation and gene function in maize. The genome, in comparison to B73, contains extensive intra-species structural variations and other genetic differences. Expression and network analyses identify discrete profiles for embryonic callus and other tissues

Genetic engineering of maize and rice to enhance tolerance against abiotic and biotic stresses

Doctor of PhilosophyDepartment of Horticulture and Natural ResourcesSunghun ParkGenetic engineering has allowed biologists to make genetic changes for crop improvement. Being sessile, plants are exposed to the different biotic and abiotic stresses throughout their life stages. Numerous genes have been studied to improve pest resistance and abiotic stress tolerance in plants. Here, we expressed Arabidopsis monothiol glutaredoxin gene in maize and studied the effect of the gene in improving drought and heat tolerance. Similarly, we expressed Pi9 gene in elite cultivar of rice to develop the resistance against blast disease through cisgenic approach. Heat and drought are two of the major abiotic stresses that usually appear simultaneously. Various climate models suggest that these stresses will increase in intensity and frequency. The reproductive phases of the development are very sensitive to both drought and high-temperature stress. Reactive oxygen species (ROS) accumulate in response to the stresses and cause oxidative damage to many biological molecules, including lipids, proteins, and DNA. In our study, we performed ectopic expression of Arabidopsis monothiol glutaredoxin, AtGRXS17, to improve tolerance against drought stress and combined heat and drought (HTD) stress at the reproductive stage of maize. Glutaredoxins (GRXs) are oxidoreductases that maintain redox homeostasis. Ectopic expression of the AtGRXS17 in maize resulted in increased tolerance against drought stress and HTD stress. Under both types of stresses, AtGRXS17-expressing maize lines showed higher yields than WT plants. Our results also indicated that AtGRXS17-expressing pollen grains showed better pollen germination than WT under desiccating environment. Despite the huge potential of genetic engineering in improving crops, concerns have been raised about the presence of foreign genes in plants and their unpredictable consequences. Because of this, commercialization of transgenic crops is highly regulated. Removing selection marker and unnecessary transgene can potentially address the biosafety concerns of regulatory bodies. In our research, we demonstrated successful incorporation of a rice blast resistance gene Pi9 into an elite US rice cultivar via cisgenic method. We used a co-transformation strategy to eliminate the marker gene (hygromycin B phosphotransferase) from the cisgenic rice. We also found that the success rate of co-transformation was very low. Nevertheless, the co-transformation approach provides an effective way to develop marker-free cisgenic plants

Ectopic Expression of a Heterologous Glutaredoxin Enhances Drought Tolerance and Grain Yield in Field Grown Maize

Drought stress is a major constraint in global maize production, causing almost 30–90% of the yield loss depending upon growth stage and the degree and duration of the stress. Here, we report that ectopic expression of Arabidopsis glutaredoxin S17 (AtGRXS17) in field grown maize conferred tolerance to drought stress during the reproductive stage, which is the most drought sensitive stage for seed set and, consequently, grain yield. AtGRXS17-expressing maize lines displayed higher seed set in the field, resulting in 2-fold and 1.5-fold increase in yield in comparison to the non-transgenic plants when challenged with drought stress at the tasseling and silking/pollination stages, respectively. AtGRXS17-expressing lines showed higher relative water content, higher chlorophyll content, and less hydrogen peroxide accumulation than wild-type (WT) control plants under drought conditions. AtGRXS17-expressing lines also exhibited at least 2-fold more pollen germination than WT plants under drought stress. Compared to the transgenic maize, WT controls accumulated higher amount of proline, indicating that WT plants were more stressed over the same period. The results present a robust and simple strategy for meeting rising yield demands in maize under water limiting conditions

Redox-engineering enhances maize thermotolerance and grain yield in the field

Increasing populations and temperatures are expected to escalate food demands beyond production capacities, and the development of maize lines with better performance under heat stress is desirable. Here, we report that constitutive ectopic expression of a heterologous glutaredoxin S17 from Arabidopsis thaliana (AtGRXS17) can provide thermotolerance in maize through enhanced chaperone activity and modulation of heat stress-associated gene expression. The thermotolerant maize lines had increased protection against protein damage and yielded a 6-fold increase in grain production in comparison to the non-transgenic counterparts under heat stress field conditions. The maize lines also displayed thermotolerance in the reproductive stages, resulting in improved pollen germination and the higher fidelity of fertilized ovules under heat stress conditions. Our results present a robust and simple strategy for meeting rising yield demands in maize and, possibly, other crop species in a warming global environment