Phosphorus (P) is an essential plant macronutrient; however, its availability is often limited in soils. Plants have evolved complex mechanisms for efficient phosphate (Pi) absorption, which are responsive to changes in external and internal Pi concentration, and orchestrated through local and systemic responses. To explore these systemic Pi responses, here, we identified AtMYB44 as a phloem-mobile mRNA, an Arabidopsis homolog of Cucumis sativus MYB44, that is responsive to the Pi-starvation stress. qRT-PCR assays revealed that AtMYB44 was up-regulated and expressed in both shoot and root in response to Pi-starvation stress. The atmyb44 mutant displayed higher shoot and root biomass, compared to wild-type plants, under Pi-starvation conditions. Interestingly, the expression of PHOSPHATE TRANSPORTER1;2 (PHT1;2) and PHT1;4 was enhanced in atmyb44 in response to a Pi-starvation treatment. A split-root assay showed that AtMYB44 expression was systemically regulated, under Pi-starvation conditions and, in atmyb44, systemic controls on PHT1;2 and PHT1;4 expression were moderately disrupted. Heterografting assays confirmed graft transmission of AtMYB44 transcripts, and PHT1;2 and PHT1;4 expression was decreased in heterografted atmyb44 rootstocks. Taken together, our findings support the hypothesis that mobile AtMYB44 mRNA serves as a long-distance Pi response signal, which negatively regulates Pi transport and utilization in Arabidopsis.

Phosphate (Pi) starvation is a critical factor limiting crop growth, development, and productivity. Rice (Oryza sativa) R2R3-MYB transcription factors function in the transcriptional regulation of plant responses to various abiotic stresses and micronutrient deprivation, but little is known about their roles in Pi starvation signaling and Pi homeostasis. Here we identified the R2R3-MYB transcription factor gene OsMYB58, which shares high sequence similarity with AtMYB58. OsMYB58 expression was induced more strongly by Pi starvation than by other micronutrient deficiencies. Overexpressing OsMYB58 in Arabidopsis thaliana and rice inhibited plant growth and development under Pi-deficiency conditions. In addition, overexpression of OsMYB58 in plants exposed to Pi deficiency strongly affected root development, including seminal root, lateral root, and root hair formation. Overexpressing OsMYB58 strongly decreased the expression of the rice microRNAs, OsmiR399a and OsmiR399j. By contrast, overexpressing OsMYB58 strongly increased the expression of rice PHOSPHATE 2 (OsPHO2), whose expression is repressed by miR399 during Pi starvation signaling. OsMYB58 functions as a transcriptional repressor of the expression of its target genes, as determined by a transcriptional activity assay. These results demonstrate that OsMYB58 negatively regulates OsmiR399-dependent Pi starvation signaling by enhancing OsmiR399s expression.

The chitin synthase B gene is a key enzyme in the chitin synthesis of insect peritrophic matrix (PM), affecting insects' feeding behavior. The chitin synthase B gene has been cloned from the transcription library of Heortia vitessoides Moore. RT-qPCR showed that HvChsb was highly expressed in the larval stage of H. vitessoides, especially on the first day of the prepupal stage, and in the midgut of larvae and the abdomen of adults. After starvation treatment, HvChsb was found to be significantly inhibited with time. After 48 h of starvation, the feeding experiment showed that HvChsb increased with the prolongation of the refeeding time. The experimental data showed that feeding affected the expression of HvChsb. HvChsb was effectively silenced by RNA interference, so its function was lost, significantly decreasing the survival rate of H. vitessoides. The survival rate from larval-to-pupal stages was only 43.33%, accompanied by abnormal phenotypes. It can be seen that HvChsb plays a key role in the average growth and development of H. vitessoides.

GCN1 is recognized as a factor that is essential for the activation of GCN2, which is a sensor of amino acid starvation. This function is evolutionarily conserved from yeast to higher eukaryotes. However, recent studies have revealed non-canonical functions of GCN1 that are independent of GCN2, such as its participation in cell proliferation, apoptosis, and the immune response, beyond the borders of species. Although it is known that GCN1 and GCN2 interact with ribosomes to accomplish amino acid starvation sensing, recent studies have reported that GCN1 binds to disomes (i.e. ribosomes that collide each other), thereby regulating both the co-translational quality control and stress response. We propose that GCN1 regulates ribosome-mediated signaling by dynamically changing its partners among RWD domain-possessing proteins via unknown mechanisms. We recently demonstrated that GCN1 is essential for cell proliferation and whole-body energy regulation in mice. However, the manner in which ribosome-initiated signaling via GCN1 is related to various physiological functions warrants clarification. GCN1-mediated mechanisms and its interaction with other quality control and stress response signals should be important for proteostasis during aging and neurodegenerative diseases, and may be targeted for drug development.

Many of the wide-ranging symptoms of COVID-19 have not been associated previously with a respiratory illness. A similarity between these atypical symptoms and the symptoms of malnutrition was observed. To investigate, a comparison of COVID-19 symptomatology with recognised states of malnutrition showed a significant relationship that was further explored in a review of the literature. This hypothesis links the atypical symptoms to the effects of increasing protein malnutrition. The rapid appearance of malnutrition symptoms at the beginning of the COVID-19 infection is concurrent with the rapid cell proliferation of the immune system. Although previous work has, in general, assumed that the body is capable of providing for the needs of the immune system during infection, heightened immune activity from the commencement of COVID-19 could require an early increase in energy yielding sources. Should insufficient availability of protein resources occur, this could quickly lead to malnutrition. Any continuing insufficiency, during the active phase of the virus, might result in widespread depletions in the tissues and the consequential malfunctioning of many organs. A new appraisal of the immune system requirements needed to counteract the impact of the novel virus, COVID-19, could show the potential benefit for earlier protein intervention in the disease process. This hypothesis could also have relevance for other life situations where a rapid cell proliferation might occur.

Ethylene is an essential plant hormone critical in various physiological processes. These processes include seed germination, leaf senescence, fruit ripening, and the plant's response to environmental stressors. Ethylene biosynthesis is tightly regulated by two key enzymes, namely 1-aminocyclopropane-1-carboxylate synthase (ACS) and 1-aminocyclopropane-1-carboxylate oxidase (ACO). Initially, the prevailing hypothesis suggested that ACS is the limiting factor in the ethylene biosynthesis pathway. Nevertheless, accumulating evidence from various studies has demonstrated that ACO, under specific circumstances, acts as the rate-limiting enzyme in ethylene production. Under normal developmental processes, ACS and ACO collaborate to maintain balanced ethylene production, ensuring proper plant growth and physiology. However, under abiotic stress conditions, such as drought, salinity, extreme temperatures, or pathogen attack, the regulation of ethylene biosynthesis becomes critical for plants’ survival. This review highlights the structural characteristics, examines the transcriptional, post-transcriptional, and post-translational regulation of ACS and ACO, and their role under abiotic stress conditions. Reviews on the role of ethylene signaling in abiotic stress adaptation are available. However, a review that delineates the role of ACS and ACO in abiotic stress acclimation is not available.

The root-colonizing endophytic fungus Piriformospora indica promotes root and shoot growth of its host plants. We show that growth promotion of Arabidopsis leaves is abolished when the seedlings are grown on media with nitrogen (N) limitation. The fungus neither stimulated the total N content nor did it promote 15NO3- uptake from agar plates to the leaves of the host under N-sufficient or N-limiting conditions. However, when the roots were co-cultivated with 15N-labelled P. indica, more label can be detected in the leaves of N-starved host plants, but not of plants supplied with sufficient N. Amino acid and primary metabolite profiles, as well as expression analyses of N metabolite transporter genes suggest that the fungus alleviates the adaptation of its host to the N limitation condition. P. indica alters the expression of transporter genes which participate in relocation of NO3-, NH4+ and N metabolites from the roots to the leaves under N limitation. We propose that P. indica participates in the plant´s metabolomic adaptation to N limitation by delivering reduced N metabolites to the host, alleviating metabolic N starvation responses, and reprogramming the expression of N-metabolism related genes.

Plants attained cellular homeostasis of phosphate (Pi) through an integrated response pathway regulated by different families of transcription factors including MYB, WRKY, bHLH and ZFP. The systemic response to Pi limitation showed the critical role played by inositol pyrophosphate (PP-InsPs) as signaling molecule and SPX (SYG1/PHO81/XPR1) domain proteins as sensor of cellular Pi status. Binding of SPX to PP-InsPs regulates the transcriptional activity of the MYB-CC proteins, phosphate starvation response factors (PHR/PHL) as the central regulator of Pi-deficiency response in plants. Vacuolar phosphate transporter, VPT may sense the cellular Pi status by its SPX domain, and vacuolar sequestration is activated under Pi replete condition and the stored Pi is an important resource to be mobilized under Pi deficiency. Proteomic approaches led to new discoveries of proteins associated with Pi-deficient response pathways and post-translational events that may influence plants in achieving Pi homeostasis. This review provides current understanding on the molecular mechanisms at the transcriptional and translational levels for achieving Pi homeostasis in plants highlighting the importance of DNA-protein and protein-protein interactions. The potential strategies for employing the CRISPR technology to modify the gene sequences of key regulatory and response proteins for attaining plant Pi homeostasis are discussed.

Lifespan extension was recently achieved in Caenorhabditis elegans nematodes by mitochondrial stress and mitophagy, triggered via iron depletion. Conversely in man, deficient mitophagy due to Pink1/Parkin mutations triggers iron accumulation in patient brain and limits survival. We now aimed to identify murine fibroblast factors, which adapt their mRNA expression to acute iron manipulation, relate to mitochondrial dysfunction and may influence survival. After iron depletion, expression of the plasma membrane receptor Tfrc with its activator Ireb2, the mitochondrial membrane transporter Abcb10, the heme-release factor Pgrmc1, the heme-degradation enzyme Hmox1, the heme-binding cholesterol metabolizer Cyp46a1, as well as the mitophagy regulators Pink1 and Parkin showed a negative correlation to iron levels. After iron overload, these factors did not change expression. Conversely, a positive correlation of mRNA levels with both conditions of iron availability was observed for the endosomal factors Slc11a2 and Steap2, as well as for the iron-sulfur-cluster (ISC)-containing factors Ppat, Bdh2 and Nthl1. Positive correlation only after iron depletion was observed for the iron export factor Slc40a1, mitochondrial iron transporters Slc25a28, Abcb7 and Abcb8, mitochondrial ISC-containing factors Glrx5, Nfu1, Bola1 and Abce1, cytosolic Aco1 and Tyw5, as well as nuclear Dna2, Elp3, Pold1 and Prim2. The latter are regulators of nucleotide synthesis and DNA quality control, which have known importance for growth and lifespan. The only Pink1-/- triggered transcript modulation was the reduced expression of the ISC-containing ribosomal factor Abce1. These mammalian findings support previous fly data that Pink1 influences co-translational quality control via Abce1, as well as mitophagy. Our findings provide the first systematic survey how iron dosage triggers homeostatic transcriptional regulations and elucidate how iron deprivation results in mitophagy.

Predicting the growth response of seedlings from the environmental responses of photosynthesis and metabolism may be improved by considering the dynamics of non-structural carbohydrate, NSC, over a diurnal cycle. Attenuation of growth metabolism when NSC content is low could explain why some NSC is conserved through the night. A dynamic model, incorporating diurnal variation in NSC, was developed to simulate growth of seedlings hour-by-hour. I compared predictions of this model to published growth and NSC data for seedlings that varied according to temperature, light, day length, or CO₂. Prolonged-darkness experiments showed a temperature dependent upper limit on the respiration capacity. Respiration was attenuated as NSC was depleted. Furthermore, when NSC was high at dawn, inhibition of photosynthesis could attenuate the accumulation of NSC under low temperature, or high light, or high CO₂. These concepts were used to simulate plant metabolism and growth rates and diurnal variation of NSC in tomato seedlings under two light levels and various temperatures. Comparison of other results using the same model parameters showed the dynamic model could predict results for starch and starch-less plants, and when growth was affected by CO₂ enrichment and day length.

Understanding the energy metabolism and its regulation is one of the clues to metabolic engineering of stress-resistant lignocellulose-converting microbial strains, including also the promising ethanologen Zymomonas mobilis. Z. mobilis is an obligately fermentative, facultatively anaerobic bacterium, carrying an active respiratory chain with a low energy-coupling efficiency. Its respiration does not supply energy to aerobically growing culture on sugary media, yet oxidative phosphorylation has been demonstrated in non-growing cells with ethanol. In the present work we show that in respiring, non-growing Z. mobilis cells, receiving regular small amounts of ethanol, oxidative phosphorylation significantly contributes to the maintenance of their viability. Accordingly, no improvement of viability is seen in the NADH dehydrogenase (ndh)-deficient respiratory mutant, unable to oxidize ethanol. The ethanol effect is hampered also by the protonophoric uncoupler CCCP, or the inhibitor of ATP synthase, DCCD. At higher concentrations (6% v/v) ethanol causes stress that slows down culture growth. By monitoring the activity of several respiratory gene promoters in aerobically growing culture under ethanol stress with the green fluorescent protein reporter system, we demonstrate downregulation of these promoters, in particular the ndh promoter. We speculate that the decrease of the respiratory chain activity mitigates the production of reactive oxygen species.