Min-Jung Yook

Uncovering the Differential Molecular Basis of Adaptive Diversity in Three Echinochloa Leaf Transcriptomes

Echinochloa is a major weed that grows almost everywhere in farmed land. This high prevalence results from its high adaptability to various water conditions, including upland and paddy fields, and its ability to grow in a wide range of climates, ranging from tropical to temperate regions. Three Echinochloa crus-galli accessions (EC-SNU1, EC-SNU2, and EC-SNU3) collected in Korea have shown diversity in their responses to flooding, with EC-SNU1 exhibiting the greatest growth among three accessions. In the search for molecular components underlying adaptive diversity among the three Echinochloa crus-galli accessions, we performed de novo assembly of leaf transcriptomes and investigated the pattern of differentially expressed genes (DEGs). Although the overall composition of the three leaf transcriptomes was well-conserved, the gene expression patterns of particular gene ontology (GO) categories were notably different among the three accessions. Under non-submergence growing conditions, five protein categories (serine/threonine kinase, leucine-rich repeat kinase, signaling-related, glycoprotein, and glycosidase) were significantly (FDR, q < 0.05) enriched in up-regulated DEGs from EC-SNU1. These up-regulated DEGs include major components of signal transduction pathways, such as receptor-like kinase (RLK) and calcium-dependent protein kinase (CDPK) genes, as well as previously known abiotic stress-responsive genes. Our results therefore suggest that diversified gene expression regulation of upstream signaling components conferred the molecular basis of adaptive diversity in Echinochloa crus-galli.

Dormancy Associated Weedy Risk of the F1 Hybrid Resulted from Gene Flow from Oilseed Rape to Mustard

To assess the dormancy associated weedy risk of the F1 hybrid generated by hybridization between Brassica juncea (maternal) and Brassica napus (paternal), seed germination, dormancy and longevity were examined sequentially after seed harvest. The F1 hybrids exhibited the intermediate characteristics of their parents in seed germination and dormancy with relatively high dormancy rate of 41.1%. In summer, F1 hybrid seeds buried in the 3 cm soil exhibited greater viability (52.4%) than those in the soil surface with greater seed longevity (74.6%) than its maternal (63.3%) and paternal (33.7%) parents at 100 days of over-summering in soil. In winter, F1 seeds buried in the soil surface were more viable than those in the 3 cm soil with greater seed longevity (83.5%) than its maternal (39.0%) and paternal (71.7%) parents at 100 days of over-wintering in soil. Therefore, it is concluded that F1 hybrid resulted from gene flow from OSR to mustard has high seed dormancy and longevity during summer and winter, suggesting its weedy risk potential. Further studies are required to examine the reproductivity and fitness cost of F1 hybrid to make a clearer conclusion of its weedy risk.

Evaluation of maximum potential gene flow from herbicide resistant Brassica napus to its male sterile relatives under open and wind pollination conditions

Pollen-mediated gene flow (PMGF) from genetically modified (GM) Brassica napus to its wild relatives by wind and insects is a major ecological concern in agricultural ecosystems. This study conducted is to estimate maximum potential gene flow and differentiate between wind- and bee-mediated gene flows from herbicide resistant (HR) B. napus to its closely-related male sterile (MS) relatives, B. napus, B. juncea and Raphanus sativus. Various markers, including pods formation in MS plants, herbicide resistance, and SSR markers, were used to identify the hybrids. Our results revealed the following: 1) maximum potential gene flow (a maximum % of the progeny of pollen recipient confirmed hybrid) to MS B. napus ranged from 32.48 to 0.30% and from 14.69 to 0.26% at 2-128 m from HR B. napus under open and wind pollination conditions, respectively, and to MS B. juncea ranged from 21.95 to 0.24% and from 6.16 to 0.16%, respectively; 2) estimates of honeybee-mediated gene flow decreased with increasing distance from HR B. napus and ranged from 17.78 to 0.03% at 2-128 m for MS B. napus and from 15.33 to 0.08% for MS B. juncea; 3) a small-scale donor plots would strongly favour insect over wind pollination; 4) no gene flow occurred from HR B. napus to MS R. sativus. Our approach and findings are helpful in understanding the relative contribution of wind and bees to gene flow and useful for estimating maximum potential gene flow and managing environmental risks associated with gene flow.

Assessment of potential environmental risks of transgene flow in smallholder farming systems in Asia: Brassica napus as a case study in Korea

The cultivation of genetically modified (GM) crops has raised many questions regarding their environmental risks, particularly about their ecological impact on non-target organisms, such as their closely-related relative species. Although evaluations of transgene flow from GM crops to their conventional crops has been conducted under large-scale farming system worldwide, in particular in North America and Australia, few studies have been conducted under smallholder farming systems in Asia with diverse crops in co-existence. A two-year field study was conducted to assess the potential environmental risks of gene flow from glufosinate-ammonium resistant (GR) Brassica napus to its conventional relatives, B. napus, B. juncea, and Raphanus sativus under simulated smallholder field conditions in Korea. Herbicide resistance and simple sequence repeat (SSR) markers were used to identify the hybrids. Hybridization frequency of B. napus × GR B. napus was 2.33% at a 2 m distance, which decreased to 0.007% at 75 m. For B. juncea, it was 0.076% at 2 m and decreased to 0.025% at 16 m. No gene flow was observed to R. sativus. The log-logistic model described hybridization frequency with increasing distance from GR B. napus to B. napus and B. juncea and predicted that the effective isolation distances for 0.01% gene flow from GR B. napus to B. napus and B. juncea were 122.5 and 23.7 m, respectively. Results suggest that long-distance gene flow from GR B. napus to B. napus and B. juncea is unlikely, but gene flow can potentially occur between adjacent fields where the smallholder farming systems exist.

Characterization of Soybean Hybrid Seeds Resulted from Natural Hybridization between LM Soybean and Wild Soybean

With increasing LM soybean import, the concern about unintentional gene flow from LM soybean to wild soybean and consequential weedy risk has been growing. Therefore, we conducted this study to characterize seed traits including germination of hybrids resulted from gene flow from LM soybean to wild soybean in comparison with their parents, LM soybean and wild soybean. Pollen-donor LM soybean seeds were much greater and heavier (about 15.0 g of 100 seed weight) than F2 hybrid (5.7 g), while pollen-recipient wild soybean and F1 hybrid seeds were smallest and lightest (about 2.5 g). F2 hybrid was brown, intermediate between yellow LM soybean seed and black wild soybean seed. These findings indicate that F1 hybrid seeds show similar characteristics with wild soybean, while F2 hybrid seeds show intermediate color and size between two parents. F2 hybrid seed showed intermediate traits between two parents in germination and dormancy rates, which were 35% and 65%, respectively. LM soybean showed no dormancy, while wild soybean showed greater than 90% dormancy. This finding indicates that F2 hybrid show intermediate characteristics in seed germination with high dormancy trait, suggesting a potential weediness of hybrids resulted from gene flow from LM soybean to wild soybean.

Adaptive Diversity of Echinochloa Species to Osmotic Stress

Three Echinochloa species inhabit various crop fields with different soil moisture conditions. Therefore, a growth pouch test was conducted to investigate adaptive diversity of six Echinochloa species, three from Korea and three from USA, to osmotic stress by assessing shoot and root growths. Echinochloa crus-galli var. praticola showed the greatest tolerance to osmotic stress in both root (GR 50 =1316.3 g PEG L −1 ) and shoot (GR 50 =212.2 g PEG L −1 ) growths, while Korean E. oryzicola was most sensitive to osmotic stress in both root (GR 50 =116 g PEG L −1 ) and shoot (GR 50 =126.2 g PEG L −1 ) growths. Root to shoot (R/S) ratio of Echinochloa crus-galli var. praticola increased with increasing osmotic stress, while that of Korean E. oryzicola decreased, suggesting that R/S ratio is closely related to osmotic stress tolerance in Echinochloa species. Our results clearly demonstrate that E. crus-galli var. praticola maintains high R/S ratio even under high osmotic stress, which enables this species to well adapt to dry upland condition. In contrast, while E. oryzicola fails to maintain sufficiently high R/S ratio, resulting in poor adaptability to dry upland condition.