Crop productivity relies heavily on nitrogen (N) fertilization. Production and application of N fertilizers consume huge amounts of energy, and excess is detrimental to the environment; therefore, increasing plant N use efficiency (NUE) is essential for the development of sustainable agriculture. Plant NUE is inherently complex, as each step—including N uptake, translocation, assimilation, and remobilization—is governed by multiple interacting genetic and environmental factors. The limiting factors in plant metabolism for maximizing NUE are different at high and low N supplies, indicating great potential for improving the NUE of current cultivars, which were bred in well-fertilized soil. Decreasing environmental losses and increasing the productivity of crop-acquired N requires the coordination of carbohydrate and N metabolism to give high yields. Increasing both the grain and N harvest index to drive N acquisition and utilization are important approaches for breeding future high-NUE cultivars.

/pdf/plant-nitrogen-assimilation-and-use-efficiency-35cshj4xrf.pdf

Plant nitrogen assimilation and use efficiency.

Unravelling cadmium toxicity and tolerance in plants: Insight into regulatory mechanisms

Mineral Nutrition of Higher Plants, 2nd edition, H. Marschner. Academic Press, London (1995), 889, (ISBN 0-12-473543-6). Price: 29.95 Pound Sterling

https://www.cell.com/trends/plant-science/pdf/S1360-1385(12)00098-2.pdf

Uptake, allocation and signaling of nitrate

A unified nomenclature of NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER family members in plants

Long-distance transport of nitrate requires xylem loading and unloading, a successive process that determines nitrate distribution and subsequent assimilation efficiency. Here, we report the functional characterization of NRT1.8, a member of the nitrate transporter (NRT1) family in Arabidopsis thaliana. NRT1.8 is upregulated by nitrate. Histochemical analysis using promoter-beta-glucuronidase fusions, as well as in situ hybridization, showed that NRT1.8 is expressed predominantly in xylem parenchyma cells within the vasculature. Transient expression of the NRT1.8:enhanced green fluorescent protein fusion in onion epidermal cells and Arabidopsis protoplasts indicated that NRT1.8 is plasma membrane localized. Electrophysiological and nitrate uptake analyses using Xenopus laevis oocytes showed that NRT1.8 mediates low-affinity nitrate uptake. Functional disruption of NRT1.8 significantly increased the nitrate concentration in xylem sap. These data together suggest that NRT1.8 functions to remove nitrate from xylem vessels. Interestingly, NRT1.8 was the only nitrate assimilatory pathway gene that was strongly upregulated by cadmium (Cd(2+)) stress in roots, and the nrt1.8-1 mutant showed a nitrate-dependent Cd(2+)-sensitive phenotype. Further analyses showed that Cd(2+) stress increases the proportion of nitrate allocated to wild-type roots compared with the nrt1.8-1 mutant. These data suggest that NRT1.8-regulated nitrate distribution plays an important role in Cd(2+) tolerance.

The Arabidopsis Nitrate Transporter NRT1.8 Functions in Nitrate Removal from the Xylem Sap and Mediates Cadmium Tolerance

Arabidopsis NRT1.5 Mediates the Suppression of Nitrate Starvation-Induced Leaf Senescence by Modulating Foliar Potassium Level

Proline plays a crucial role in the drought stress response in plants. However, there are still gaps in our knowledge about the molecular mechanisms that regulate proline metabolism under drought stress. Here, we report that the histone methylase encoded by CAU1, which is genetically upstream of P5CS1 (encoding the proline biosynthetic enzyme Δ1-pyrroline-5-carboxylate synthetase 1), plays a crucial role in proline-mediated drought tolerance. We determined that the transcript level of CAU1 decreased while that of ANAC055 (encoding a transcription factor) increased in wild-type Arabidopsis under drought stress. Further analyses showed that CAU1 bound to the promoter of ANAC055 and suppressed its expression via H4R3sme2-type histone methylation in the promoter region. Thus, under drought stress, a decreased level of CAU1 led to an increased transcript level of ANAC055, which induced the expression of P5CS1 and increased proline level independently of CAS. Drought tolerance and the level of proline were found to be decreased in the cau1 anac055 double-mutant, while proline supplementation restored drought sensitivity in the anac055 mutant. Our results reveal the details of a novel pathway leading to drought tolerance mediated by CAU1.

/pdf/control-of-proline-accumulation-under-drought-via-a-novel-45ofekj7nd.pdf

Control of proline accumulation under drought via a novel pathway comprising the histone methylase CAU1 and the transcription factor ANAC055.

Elevations in extracellular calcium ([Ca2+]o) are known to stimulate cytosolic calcium ([Ca2+]cyt) oscillations to close stomata. However, the underlying mechanisms regulating this process remain largely to be determined. Here, through the functional characterization of the calcium underaccumulation mutant cau1, we report that the epigenetic regulation of CAS, a putative Ca2+ binding protein proposed to be an external Ca2+ sensor, is involved in this process. cau1 mutant plants display increased drought tolerance and stomatal closure. A mutation in CAU1 significantly increased the expression level of the calcium signaling gene CAS, and functional disruption of CAS abolished the enhanced drought tolerance and stomatal [Ca2+]o signaling in cau1. Map-based cloning revealed that CAU1 encodes the H4R3sme2 (for histone H4 Arg 3 with symmetric dimethylation)-type histone methylase protein arginine methytransferase5/Shk1 binding protein1. Chromatin immunoprecipitation assays showed that CAU1 binds to the CAS promoter and modulates the H4R3sme2-type histone methylation of the CAS chromatin. When exposed to elevated [Ca2+]o, the protein levels of CAU1 decreased and less CAU1 bound to the CAS promoter. In addition, the methylation level of H4R3sme2 decreased in the CAS chromatin. Together, these data suggest that in response to increases in [Ca2+]o, fewer CAU1 protein molecules bind to the CAS promoter, leading to decreased H4R3sme2 methylation and consequent derepression of the expression of CAS to mediate stomatal closure and drought tolerance.

Arabidopsis Histone Methylase CAU1/PRMT5/SKB1 Acts as an Epigenetic Suppressor of the Calcium Signaling Gene CAS to Mediate Stomatal Closure in Response to Extracellular Calcium

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/j.febslet.2015.03.016

Yan-Lei Fu

Papers

The Arabidopsis Nitrate Transporter NRT1.8 Functions in Nitrate Removal from the Xylem Sap and Mediates Cadmium Tolerance

Arabidopsis NRT1.5 Mediates the Suppression of Nitrate Starvation-Induced Leaf Senescence by Modulating Foliar Potassium Level

Control of proline accumulation under drought via a novel pathway comprising the histone methylase CAU1 and the transcription factor ANAC055.

Arabidopsis Histone Methylase CAU1/PRMT5/SKB1 Acts as an Epigenetic Suppressor of the Calcium Signaling Gene CAS to Mediate Stomatal Closure in Response to Extracellular Calcium

LeNRT2.3 functions in nitrate acquisition and long-distance transport in tomato.