Down-regulation of the rice HRS1 HOMOLOG3 transcriptional repressor gene due to N deficiency directly co-activates ammonium and phosphate transporter genes.

Rice HRS1 HOMOLOG3 (OsHHO3) acts as a transcriptional repressor of AMMONIUM TRANSPORTER1 (OsAMT1) genes in rice; thus, reduced OsHHO3 expression in nitrogen (N)-deficient environments promotes ammonium uptake. In this study, we show that OsHHO3 also functions as a repressor of a specific subset of phosphate (Pi) transporter (PT) genes involved in the uptake and root-to-shoot translocation of Pi, including OsPT2, OsPT4, and OsPHO1;1. Disruption of OsHHO3 increased Pi uptake and Pi contents in shoots and roots, while overexpression of OsHHO3 caused the opposite effects.

HASTY-mediated miRNA dynamics modulate nitrogen starvation-induced leaf senescence in Arabidopsis.

Nitrogen (N) deficiency responses are essential for plant survival and reproduction. Here, via an expression genome-wide association study (eGWAS), we reveal a mechanism that regulates microRNA (miRNA) dynamics necessary for N deficiency responses in Arabidopsis. Differential expression levels of three NAC transcription factor (TF) genes involved in leaf N deficiency responses among Arabidopsis accessions are most significantly associated with polymorphisms in HASTY (HST), which encodes an importin/exportin family protein responsible for the generation of mature miRNAs.

Dof1.7 and NIGT1 transcription factors mediate multilayered transcriptional regulation for different expression patterns of NITRATE TRANSPORTER2 genes under nitrogen deficiency stress.

Elucidating the mechanisms regulating nitrogen (N) deficiency responses in plants is of great agricultural importance. Previous studies revealed that decreased expression of NITRATE-INDUCIBLE GARP-TYPE TRANSCRIPTIONAL REPRESSOR1 (NIGT1) transcriptional repressor genes upon N deficiency is involved in N deficiency-inducible gene expression in Arabidopsis thaliana. However, our knowledge of the mechanisms controlling N deficiency-induced changes in gene expression is still limited.

Arabidopsis BBX14 negatively regulates nitrogen starvation- and dark-induced leaf senescence.

Senescence is a highly regulated process driven by developmental age and environmental factors. Although leaf senescence is accelerated by nitrogen (N) deficiency, the underlying physiological and molecular mechanisms are largely unknown. Here, we reveal that BBX14, a previously uncharacterized BBX-type transcription factor in Arabidopsis, is crucial for N starvation-induced leaf senescence.

The Arabidopsis NLP7-HB52/54-VAR2 pathway modulates energy utilization in diverse light and nitrogen conditions.

In plants, nitrate is the dominant nitrogen (N) source and a critical nutrient signal regulating various physiological and developmental processes. Nitrate-responsive gene regulatory networks are widely believed to control growth, development, and life cycle in addition to N acquisition and utilization, and NIN-LIKE PROTEIN (NLP) transcriptional activators have been identified as the master regulators governing the networks. However, it remains to be elucidated how nitrate signaling regulates respective physiological and developmental processes.

Molecular basis of nitrogen starvation-induced leaf senescence.

Nitrogen (N), a macronutrient, is often a limiting factor in plant growth, development, and productivity. To adapt to N-deficient environments, plants have developed elaborate N starvation responses. Under N-deficient conditions, older leaves exhibit yellowing, owing to the degradation of proteins and chlorophyll pigments in chloroplasts and subsequent N remobilization from older leaves to younger leaves and developing organs to sustain plant growth and productivity.

RWP-RK domain-containing transcription factors in the Viridiplantae: biology and phylogenetic relationships.

The RWP-RK protein family is a group of transcription factors containing the RWP-RK DNA-binding domain. This domain is an ancient motif that emerged before the establishment of the Viridiplantae-the green plants, consisting of green algae and land plants. The domain is mostly absent in other kingdoms but widely distributed in Viridiplantae.

Arabidopsis nitrate-induced aspartate oxidase gene expression is necessary to maintain metabolic balance under nitrogen nutrient fluctuation.

Nitrate is a nutrient signal that regulates growth and development through NLP transcription factors in plants. Here we identify the L-aspartate oxidase gene (AO) necessary for de novo NAD biosynthesis as an NLP target in Arabidopsis. We investigated the physiological significance of nitrate-induced AO expression by expressing AO under the control of the mutant AO promoter lacking the NLP-binding site in the ao mutant.

Light-Mediated Regulation of Leaf Senescence.

Light is the primary regulator of various biological processes during the plant life cycle. Although plants utilize photosynthetically active radiation to generate chemical energy, they possess several photoreceptors that perceive light of specific wavelengths and then induce wavelength-specific responses. Light is also one of the key determinants of the initiation of leaf senescence, the last stage of leaf development.

Enhanced NRT1.1/NPF6.3 expression in shoots improves growth under nitrogen deficiency stress in Arabidopsis.

Identification of genes and their alleles capable of improving plant growth under low nitrogen (N) conditions is key for developing sustainable agriculture. Here, we show that a genome-wide association study using Arabidopsis thaliana accessions suggested an association between different magnitudes of N deficiency responses and diversity in NRT1.1/NPF6.

Environmental Control of Phosphorus Acquisition: A Piece of the Molecular Framework Underlying Nutritional Homeostasis.

Homeostasis of phosphorus (P), an essential macronutrient, is vital for plant growth under diverse environmental conditions. Although plants acquire P from the soil as inorganic phosphate (Pi), its availability is generally limited. Therefore, plants employ mechanisms involving various Pi transporters that facilitate efficient Pi uptake against a steep concentration gradient across the plant-soil interface.

NIGT1 family proteins exhibit dual mode DNA recognition to regulate nutrient response-associated genes in Arabidopsis.

Fine-tuning of nutrient uptake and response is indispensable for maintenance of nutrient homeostasis in plants, but the details of underlying mechanisms remain to be elucidated. NITRATE-INDUCIBLE GARP-TYPE TRANSCRIPTIONAL REPRESSOR 1 (NIGT1) family proteins are plant-specific transcriptional repressors that function as an important hub in the nutrient signaling network associated with the acquisition and use of nitrogen and phosphorus. Here, by yeast two-hybrid assays, bimolecular fluorescence complementation assays, and biochemical analysis with recombinant proteins, we show that Arabidopsis NIGT1 family proteins form a dimer via the interaction mediated by a coiled-coil domain (CCD) in their N-terminal regions.

Rice ETHYLENE RESPONSE FACTOR 101 Promotes Leaf Senescence Through Jasmonic Acid-Mediated Regulation of and .

Leaf senescence is the final stage of leaf development and an important step that relocates nutrients for grain filling in cereal crops. Senescence occurs in an age-dependent manner and under unfavorable environmental conditions such as deep shade, water deficit, and high salinity stresses. Although many transcription factors that modulate leaf senescence have been identified, the mechanisms that regulate leaf senescence in response to environmental conditions remain elusive.

Multilayered Regulation of Membrane-Bound ONAC054 Is Essential for Abscisic Acid-Induced Leaf Senescence in Rice.

In most plants, abscisic acid (ABA) induces premature leaf senescence; however, the mechanisms of ABA signaling during leaf senescence remain largely unknown. Here, we show that the rice () NAM/ATAF1/2/CUC2 (NAC) transcription factor ONAC054 plays an important role in ABA-induced leaf senescence. The knockout mutants maintained green leaves, while -overexpressing lines showed early leaf yellowing under dark- and ABA-induced senescence conditions.

A Jasmonate-Activated MYC2-Dof2.1-MYC2 Transcriptional Loop Promotes Leaf Senescence in Arabidopsis.

DNA binding-with-one-finger (Dof) proteins are plant-specific transcription factors closely associated with a variety of physiological processes. Here, we show that the Dof protein family in Arabidopsis () functions in leaf senescence. Disruption of , a jasmonate (JA)-inducible gene, led to a marked reduction in promotion of leaf senescence and inhibition of root development as well as dark-induced and age-dependent leaf senescence, while overexpression of promoted these processes.

Transgenic expression of rice MYB102 (OsMYB102) delays leaf senescence and decreases abiotic stress tolerance in Arabidopsis thaliana.

MYB-type transcription factors (TFs) play important roles in plant growth and development, and in the rapid responses to unfavorable environmental conditions. We recently reported the isolation and characterization of a rice (Oryza sativa) MYB TF, OsMYB102, which is involved in the regulation of leaf senescence by downregulating abscisic acid (ABA) biosynthesis and the downstream signaling response. Based on the similarities of their sequences and expression patterns, OsMYB102 appears to be a homolog of the Arabidopsis thaliana AtMYB44 TF.

Rice transcription factor OsMYB102 delays leaf senescence by down-regulating abscisic acid accumulation and signaling.

MYB-type transcription factors (TFs) play important roles in plant growth and development, and in the responses to several abiotic stresses. In rice (Oryza sativa), the roles of MYB-related TFs in leaf senescence are not well documented. Here, we examined rice MYB TF gene OsMYB102 and found that an OsMYB102 T-DNA activation-tagged line (termed osmyb102-D), which constitutively expresses OsMYB102 under the control of four tandem repeats of the 35S promoter, and OsMYB102-overexpressing transgenic lines (35S:OsMYB102 and 35S:GFP-OsMYB102) maintain green leaves much longer than the wild-type under natural, dark-induced, and abscisic acid (ABA)-induced senescence conditions.

A phytochrome-B-mediated regulatory mechanism of phosphorus acquisition.

Phosphorus (P) is a key macronutrient whose availability has a profound effect on plant growth and productivity. The understanding of the mechanism underlying P availability-responsive P acquisition has expanded largely in the past decade; however, effects of other environmental factors on P acquisition and utilization remain elusive. Here, by imaging natural variation in phosphate uptake in 200 natural accessions of Arabidopsis, we identify two accessions with low phosphate uptake activity, Lm-2 and CSHL-5.

A NIGT1-centred transcriptional cascade regulates nitrate signalling and incorporates phosphorus starvation signals in Arabidopsis.

Nitrate is a nutrient signal that triggers complex regulation of transcriptional networks to modulate nutrient-dependent growth and development in plants. This includes time- and nitrate concentration-dependent regulation of nitrate-related gene expression. However, the underlying mechanisms remain poorly understood.

Salt Treatments and Induction of Senescence.

High salinity, one of the most severe abiotic stresses encountered by land plants, often results from water deficit and also induces whole-plant senescence. Thus, salt treatment provides a useful technique for stress-mediated induction of senescence in plants. In this chapter, we describe the procedures to induce senescence in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), using NaCl or KCl.

Light signalling-induced regulation of nutrient acquisition and utilisation in plants.

Light is the foremost regulator of plant growth and development, and the critical role of light signalling in the promotion of nutrient uptake and utilisation was clarified in recent decades. Recent studies with Arabidopsis demonstrated the molecular mechanisms underlying such promotive effects and uncovered the pivotal role of the transcription factor ELONGATED HYPOCOTYL5 (HY5) whose activity is under the control of multiple photoreceptors. Together with a recent finding that phytochrome B, one of photoreceptors, is activated in subterranean plant parts, the discovery that HY5 directly promotes the transcription of genes involved in nutrient uptake and utilisation, including several nitrogen and sulphur assimilation-related genes, expands our understanding of the ways in which light signalling effectively and co-ordinately modulates uptake and utilisation of multiple nutrients in plants.

The F-box protein FKF1 inhibits dimerization of COP1 in the control of photoperiodic flowering.

In Arabidopsis thaliana, CONSTANS (CO) plays an essential role in the regulation of photoperiodic flowering under long-day conditions. CO protein is stable only in the afternoon of long days, when it induces the expression of FLOWERING LOCUS T (FT), which promotes flowering. The blue-light photoreceptor FLAVIN-BINDING, KELCH REPEAT, F-BOX1 (FKF1) interacts with CO and stabilizes it by an unknown mechanism.