School of BioSciences - Research Publications
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ItemOsEIL1 protects rice growth under NH4+ nutrition by regulating OsVTC1-3-dependent N-glycosylation and root NH4+ efflux(WILEY, 2022-05)Rice is known for its superior adaptation to ammonium (NH4+ ) as a nitrogen source. Compared to many other cereals, it displays lower NH4+ efflux in roots and higher nitrogen-use efficiency on NH4+ . A critical role for GDP-mannose pyrophosphorylase (VTC1) in controlling root NH4+ fluxes was previously documented in Arabidopsis, but the molecular pathways involved in regulating VTC1-dependent NH4+ efflux remain unclear. Here, we report that ETHYLENE-INSENSITIVE3-LIKE1 (OsEIL1) acts as a key transcription factor regulating OsVTC1-3-dependent NH4+ efflux and protein N-glycosylation in rice grown under NH4+ nutrition. We show that OsEIL1 in rice plays a contrasting role to Arabidopsis-homologous ETHYLENE-INSENSITIVE3 (AtEIN3) and maintains rice growth under NH4+ by stabilizing protein N-glycosylation and reducing root NH4+ efflux. OsEIL1 constrains NH4+ efflux by activation of OsVTC1-3, but not OsVTC1-1 or OsVTC1-8. OsEIL1 binds directly to the promoter EIN3-binding site (EBS) of OsVTC1-3 in vitro and in vivo and acts to increase the transcription of OsVTC1-3. Our work demonstrates an important link between excessive root NH4+ efflux and OsVTC1-3-mediated protein N-glycosylation in rice grown under NH4+ nutrition and identifies OsEIL1 as a direct genetic regulator of OsVTC1-3 expression.
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ItemSyringic acid from rice roots inhibits soil nitrification and N2O emission under red and paddy soils but not a calcareous soil.(Frontiers Media S.A., 2022)Syringic acid (SA) is a novel biological nitrification inhibitor (BNIs) discovered in rice root exudates with significant inhibition of Nitrosomonas strains. However, the inhibitory effect of SA on nitrification and nitrous oxide (N2O) emissions in different soils and the environmental factors controlling the degree of inhibition have not been studied. Using 14-day microcosm incubation, we investigated the effects of different concentrations of SA on nitrification activity, abundance of ammonia-oxidizing microorganisms, and N2O emissions in three typical agricultural soils. The nitrification inhibitory efficacy of SA was strongest in acidic red soil, followed by weakly acidic paddy soil, with no significant effect in an alkaline calcareous soil. Potential nitrification activity (PNA) were also greatly reduced by SA additions in paddy and red soil. Pearson correlation analysis showed that the inhibitory efficacy of SA might be negatively correlated with soil pH and positively correlated with clay percentage. SA treatments significantly reduced N2O emissions by 69.1-79.3% from paddy soil and by 40.8%-46.4% from red soil, respectively, but no effect was recorded in the calcareous soil. SA addition possessed dual inhibition of both ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) abundance in paddy and red soil. Structural equation modelling revealed that soil ammonium (NH4 +) and dissolved organic carbon content (DOC) were the key variables explaining AOA and AOB abundance and subsequent N2O emissions. Our results support the potential for the use of the BNI SA in mitigating N2O emissions and enhancing N utilization in red and paddy soils.
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ItemThe Role of Plant Growth Regulators in Modulating Root Architecture and Tolerance to High-Nitrate Stress in Tomato(FRONTIERS MEDIA SA, 2022-04-08)Plant growth regulators are known to exert strong influences on plant performance under abiotic stress, including exposure to high nitrate, as occurs commonly in intensive vegetable production. However, direct comparative evaluations of growth regulators under otherwise identical conditions in major crop species are scarce. In this study, tomato (Solanum lycopersicum L.) was used as a model crop, and the roles of four common exogenously applied plant growth regulators (MT, melatonin; SA, salicylic acid; HA, humic acid; SNP, sodium nitroprusside) in regulating crop growth were studied under high-nitrate stress. We provide a particular focus on root system architecture and root physiological responses. Our data show that all four growth regulators improve tomato tolerance under high nitrate, but that this occurs to differing extents and via differing mechanisms. Optimal concentrations of MT, SA, HA, and SNP were 50 μmol L-1, 25 μmol L-1, 25 mg L-1, and 50 μmol L-1, respectively. MT and SNP produced the strongest effects. MT enhanced root growth while SNP enhanced above-ground growth. Growth of coarse and thin lateral roots was significantly improved. Furthermore, an enhancement of root vitality and metabolism, improved integrity of root cell membranes, and an increase in antioxidant enzyme activities were found, but regulatory mechanisms were different for each growth regulator. Our results show that in particular the application of MT and SNP can improve growth of tomato in intensive vegetable production under high-nitrate stress and that root growth stimulation is of special importance in procuring these beneficial effects.
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ItemBiological nitrification inhibition by rice root exudates and its relationship with nitrogen-use efficiency(WILEY, 2016-11)Microbial nitrification in soils is a major contributor to nitrogen (N) loss in agricultural systems. Some plants can secrete organic substances that act as biological nitrification inhibitors (BNIs), and a small number of BNIs have been identified and characterized. However, virtually no research has focused on the important food crop, rice (Oryza sativa). Here, 19 rice varieties were explored for BNI potential on the key nitrifying bacterium Nitrosomonas europaea. Exudates from both indica and japonica genotypes were found to possess strong BNI potential. Older seedlings had higher BNI abilities than younger ones; Zhongjiu25 (ZJ25) and Wuyunjing7 (WYJ7) were the most effective genotypes among indica and japonica varieties, respectively. A new nitrification inhibitor, 1,9-decanediol, was identified, shown to block the ammonia monooxygenase (AMO) pathway of ammonia oxidation and to possess an 80% effective dose (ED80 ) of 90 ng μl-1 . Plant N-use efficiency (NUE) was determined using a 15 N-labeling method. Correlation analyses indicated that both BNI abilities and 1,9-decanediol amounts of root exudates were positively correlated with plant ammonium-use efficiency and ammonium preference. These findings provide important new insights into the plant-bacterial interactions involved in the soil N cycle, and improve our understanding of the BNI capacity of rice in the context of NUE.
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ItemThe nitrogen-potassium intersection: membranes, metabolism, and mechanism(WILEY, 2017-10)Nitrogen (N) and potassium (K) are the two most abundantly acquired mineral elements by plants, and their acquisition pathways interact in complex ways. Here, we review pivotal interactions with respect to root acquisition, storage, translocation and metabolism, between the K+ ion and the two major N sources, ammonium (NH4+ ) and nitrate (NO3- ). The intersections between N and K physiology are explored at a number of organizational levels, from molecular-genetic processes, to compartmentation, to whole plant physiology, and discussed in the context of both N-K cooperation and antagonism. Nutritional regulation and optimization of plant growth, yield, metabolism and water-use efficiency are also discussed.
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ItemThe controversies of silicon’s role in plant biology(Wiley-Blackwell Publishing, 2019-01-01)Silicon (Si) is not classified as an essential plant nutrient, and yet numerous reports have shown its beneficial effects in a variety of species and environmental circumstances. This has created much confusion in the scientific community with respect to its biological roles. Here, we link molecular and phenotypic data to better classify Si transport, and critically summarize the current state of understanding of the roles of Si in higher plants. We argue that much of the empirical evidence, in particular that derived from recent functional genomics, is at odds with many of the mechanistic assertions surrounding Si's role. In essence, these data do not support reports that Si affects a wide range of molecular‐genetic, biochemical and physiological processes. A major reinterpretation of Si's role is therefore needed, which is critical to guide future studies and inform agricultural practice. We propose a working model, which we term the ‘apoplastic obstruction hypothesis’, which attempts to unify the various observations on Si's beneficial influences on plant growth and yield. This model argues for a fundamental role of Si as an extracellular prophylactic agent against biotic and abiotic stresses (as opposed to an active cellular agent), with important cascading effects on plant form and function.
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ItemExcess iron stress reduces root tip zone growth through nitric oxide-mediated repression of potassium homeostasis in Arabidopsis(WILEY, 2018-07)The root tip zone is regarded as the principal action site for iron (Fe) toxicity and is more sensitive than other root zones, but the mechanism underpinning this remains largely unknown. We explored the mechanism underpinning the higher sensitivity at the Arabidopsis root tip and elucidated the role of nitric oxide (NO) using NO-related mutants and pharmacological methods. Higher Fe sensitivity of the root tip is associated with reduced potassium (K+ ) retention. NO in root tips is increased significantly above levels elsewhere in the root and is involved in the arrest of primary root tip zone growth under excess Fe, at least in part related to NO-induced K+ loss via SNO1 (sensitive to nitric oxide 1)/SOS4 (salt overly sensitive 4) and reduced root tip zone cell viability. Moreover, ethylene can antagonize excess Fe-inhibited root growth and K+ efflux, in part by the control of root tip NO levels. We conclude that excess Fe attenuates root growth by effecting an increase in root tip zone NO, and that this attenuation is related to NO-mediated alterations in K+ homeostasis, partly via SNO1/SOS4.
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ItemContinuous monitoring of plant sodium transport dynamics using clinical PET(BMC, 2021-01-19)BACKGROUND: The absorption, translocation, accumulation and excretion of substances are fundamental processes in all organisms including plants, and have been successfully studied using radiotracers labelled with 11C, 13N, 14C and 22Na since 1939. Sodium is one of the most damaging ions to the growth and productivity of crops. Due to the significance of understanding sodium transport in plants, a significant number of studies have been carried out to examine sodium influx, compartmentation, and efflux using 22Na- or 24Na-labeled salts. Notably, however, most of these studies employed destructive methods, which has limited our understanding of sodium flux and distribution characteristics in real time, in live plants. Positron emission tomography (PET) has been used successfully in medical research and diagnosis for decades. Due to its ability to visualise and assess physiological and metabolic function, PET imaging has also begun to be employed in plant research. Here, we report the use of a clinical PET scanner with a 22Na tracer to examine 22Na-influx dynamics in barley plants (Hordeum vulgare L. spp. Vulgare-cultivar Bass) under variable nutrient levels, alterations in the day/night light cycle, and the presence of sodium channel inhibitors. RESULTS: 3D dynamic PET images of whole plants show readily visible 22Na translocation from roots to shoots in each examined plant, with rates influenced by both nutrient status and channel inhibition. PET images show that plants cultivated in low-nutrient media transport more 22Na than plants cultivated in high-nutrient media, and that 22Na uptake is suppressed in the presence of a cation-channel inhibitor. A distinct diurnal pattern of 22Na influx was discernible in curves displaying rates of change of relative radioactivity. Plants were found to absorb more 22Na during the light period, and anticipate the change in the light/dark cycle by adjusting the sodium influx rate downward in the dark period, an effect not previously described experimentally. CONCLUSIONS: We demonstrate the utility of clinical PET/CT scanners for real-time monitoring of the temporal dynamics of sodium transport in plants. The effects of nutrient deprivation and of ion channel inhibition on sodium influx into barley plants are shown in two proof-of-concept experiments, along with the first-ever 3D-imaging of the light and dark sodium uptake cycles in plants. This method carries significant potential for plant biology research and, in particular, in the context of genetic and treatment effects on sodium acquisition and toxicity in plants.
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ItemSelenium Biofortification and Interaction With Other Elements in Plants: A Review(FRONTIERS MEDIA SA, 2020-11-05)Selenium (Se) is an essential element for humans and animals and its deficiency in the diet is a global problem. Crop plants are the main source of Se for consumers. Therefore, there is much interest in understanding the factors that govern the accumulation and distribution of Se in the tissues of crop plants and the mechanisms of interaction of Se absorption and accumulation with other elements, especially with a view toward optimizing Se biofortification. An ideal crop for human consumption is rich in essential nutrient elements such as Se, while showing reduced accumulation of toxic elements in its edible parts. This review focuses on (a) summarizing the nutritional functions of Se and the current understanding of Se uptake by plant roots, translocation of Se from roots to shoots, and accumulation of Se in grains; and (b) discussing the influence of nitrogen (N), phosphorus (P), and sulfur (S) on the biofortification of Se. In addition, we discuss interactions of Se with major toxicant metals (Hg, As, and Cd) frequently present in soil. We highlight key challenges in the quest to improve Se biofortification, with a focus on both agronomic practice and human health.