Photosynthetic assimilation of CO2 regulates TOR activity

The target of rapamycin (TOR) kinase is a master regulator that integrates nutrient signals to promote cell growth in all eukaryotes. It is well established that amino acids and glucose are major regulators of TOR signaling in yeast and metazoan, but whether and how TOR responds to carbon availability in photosynthetic organisms is less understood. In this study, we showed that photosynthetic assimilation of CO2 by the Calvin–Benson–Bassham (CBB) cycle regulates TOR activity in the model single-celled microalga Chlamydomonas reinhardtii. Stimulation of CO2 fixation boosted TOR activity, whereas inhibition of the CBB cycle and photosynthesis down-regulated TOR. We uncovered a tight link between TOR activity and the endogenous level of a set of amino acids including Ala, Glu, Gln, Leu, and Val through the modulation of CO2 fixation and the use of amino acid synthesis inhibitors. Moreover, the finding that the Chlamydomonas starch-deficient mutant sta6 displayed disproportionate TOR activity and high levels of most amino acids, particularly Gln, further connected carbon assimilation and amino acids to TOR signaling. Thus, our results showed that CO2 fixation regulates TOR signaling, likely through the synthesis of key amino acids.

Profiling of associated proteins reveals dual functions of the phosphatase ABI1 in abscisic acid signaling

Clade A PP2C phosphatases are central components of the ABA-receptor coupled core signaling pathway, and are involved in multiple stress responses and developmental processes. However, the direct targets or partner proteins of A clade PP2Cs that participate in these biological processes are largely unknown. Here, we used a TurboID-based proximity labeling method to identify putative associated proteins of one A clade PP2C phosphatase, ABI1. By combining the results from affinity purification or proximity labeling of biotinylated proteins, we identified more than four hundred putative ABI1-associated proteins, including dozens of known ABI1-intreacting proteins, as well as proteins involved in TOR signaling, phospho-regulation, and other biological processes. We found that RAFs, a group of protein kinases that phosphorylate and activate SnRK2s in ABA and osmotic stress signaling, are direct substrates of ABI1. A conserved serine residue located in the P-loop of the kinase domain, corresponding to Ser619 in RAF3, is a major functional ABI1 target site. ABI1-mediated dephosphorylation on this site strongly promotes the kinase activity of most B2 and B3 RAFs. Thus, ABI1 has dual functions in ABA signaling by dephosphorylating and inhibiting SnRK2 to prevent SnRK2 activation in unstressed conditions, while dephosphorylating B2 and B3 subgroup RAFs to maintain their basal kinase activity. PP2C-mediated dephosphorylation at the conserved serine residue may be a mechanism for RAF activation in both plants and animals, with potential implications for tumorigenesis in humans.

Dietary valine improved growth, immunity, enzymatic activities and expression of TOR signaling cascade genes in rainbow trout, Oncorhynchus mykiss fingerlings

This study was conducted to determine the effects of dietary valine (Val) on growth, hemato-biochemical parameters, immunity, enzymatic activities, antioxidant status and expression of target of rapamycin (TOR) and 4E-BP genes in rainbow trout, Oncorhynchus mykiss (1.57 ± 0.03 g; 5.10 ± 0.34 cm). Six isonitrogenous (450 g kg−1) and isoenergetic (20.90 kJ 100 g−1, gross energy) diets were designed to represent varied Val levels (10.5, 13.0, 15.5, 18.0, 20.5 and 23.0 g kg−1 dry diet basis). Growth parameters improved significantly (P < 0.05) with the amelioration of dietary Val level up to 18.0 g kg−1. Highest (P < 0.05) body protein content was noted at 18.0 g kg−1 dietary Val. Significant differences in hematological, intestinal enzymatic activities and antioxidant parameters were noted. However, plasma variables did not show any significant differences except aspartate transaminase and uric acid. Total protein content increased significantly, while the albumin and globulin content did not show any significant (P > 0.05) difference. Moreover expression of TOR mRNA and elF4E-binding protein (4E-BP) was observed higher (P < 0.05) at 18.0 g kg−1 Val. On the basis of results, optimum dietary Val requirement for maximal growth of rainbow trout was determined to be 18.19 g kg−1 of dry diet, corresponding to 40.42 g kg−1 of dietary protein.

Auxin and Target of Rapamycin Spatiotemporally Regulate Root Organogenesis

The programs associated with embryonic roots (ERs), primary roots (PRs), lateral roots (LRs), and adventitious roots (ARs) play crucial roles in the growth and development of roots in plants. The root functions are involved in diverse processes such as water and nutrient absorption and their utilization, the storage of photosynthetic products, and stress tolerance. Hormones and signaling pathways play regulatory roles during root development. Among these, auxin is the most important hormone regulating root development. The target of rapamycin (TOR) signaling pathway has also been shown to play a key role in root developmental programs. In this article, the milestones and influential progress of studying crosstalk between auxin and TOR during the development of ERs, PRs, LRs and ARs, as well as their functional implications in root morphogenesis, development, and architecture, are systematically summarized and discussed.

Neuropeptide Bursicon Influences Reproductive Physiology in Tribolium Castaneum

Bursicon is a neuropeptide belonging to the cystine knot family and is composed of burs and partner of burs (pburs) subunits. It can form heterodimers or homodimers to execute different biological functions. Bursicon heterodimers regulate cuticle sclerotization and wing maturation, whereas bursicon homodimers mediate innate immunity and midgut stem cell proliferation. A recent study has shown that bursicon potentially induces the expression of vitellogenin (Vg) in the black tiger shrimp Penaeus monodon; however, the underlying mechanism remains unknown. In this study, we investigated the role of bursicon in the reproductive physiology of the red flour beetle, Tribolium castaneum. The knockdown of burs, pburs, or its receptor T. castaneum rickets (Tcrk) in 2-day pupae significantly downregulated the expression levels of Vg1, Vg2, and Vg receptor (VgR) genes in females 3- and 5-day post-adult emergence, leading to abnormal oocytes with limited Vg content. The silencing of burs repressed the number of eggs laid and completely inhibited egg hatch, whereas the silencing of pburs dramatically decreased the number of eggs laid, hatch rate, and offspring larval size, and this RNA interference (RNAi) effects persisted to the next generation. Furthermore, the knockdown of burs or pburs downregulated the expression of the insulin/insulin-like signaling/target of rapamycin (TOR) signaling genes encoding insulin receptor (InR), protein kinase B (Akt), TOR, and ribosomal protein S6 kinase (S6K). Most importantly, the injection of recombinant pburs (r-pburs) protein was able to upregulate the expression of Vg, VgR, InR, Akt, TOR, S6K, JH synthesis (JHAMT), Methoprene-tolerant (Met), and Taiman (Tai) in normal females and rescue the expression of Vg and VgR in pburs RNAi females but failed to rescue Vg and VgR in Tcrk knockdown females. We infer that bursicon homodimers influence Vg expression via the receptor Tcrk, possibly by mediating the expression of the juvenile hormone (JH) and IIS/TOR pathway genes, thereby regulating reproduction in T. castaneum.

Azospirillum brasilense stimulate the growth in Arabidopsis thaliana through the target of rapamycin protein

Azospirillum spp., one of the best studied genus of plant growth promoting rhizobacteria. These rhizobacteria are able to colonize hundreds of plant species and improve their growth, development and productivity. The target of rapamycin (TOR) protein is a central component of the TOR signaling pathway, which regulates cell growth and metabolism in response to environment cues in eukaryotes. In this study, the TOR function was analyzed in Arabidopsis thaliana L. plants inoculated with the rhizobacteria Azospirillum brasilense. Arabidopsis seedlings tor-es, which express an interference RNA in presence of estradiol and decrease TOR expression, showed an inhibition in the growth and lateral root formation, with or without 1x102 CFU/mL of the inoculum. In addition, a morphological analysis of the root showed an inhibition in the root hair formation. The results suggest that A. brasilense controls A. thaliana growth through TOR signaling pathway.

Arginine Regulates TOR Signaling Pathway through SLC38A9 in Abalone Haliotis discus hannai

Arginine plays an important role in the regulation of the target of the rapamycin (TOR) signaling pathway, and Solute Carrier Family 38 Member 9 (SLC38A9) was identified to participate in the amino acid-dependent activation of TOR in humans. However, the regulations of arginine on the TOR signaling pathway in abalone are still unclear. In this study, slc38a9 of abalone was cloned, and the slc38a9 was knocked down and overexpressed to explore its function in the regulation of the TOR signaling pathway. The results showed that knockdown of slc38a9 decreased the expression of tor, ribosomal s6 protein kinase (s6k) and eukaryotic translation initiation factor 4e (eif4e) and inhibited the activation of the TOR signaling pathway by arginine. Overexpression of slc38a9 up-regulated the expression of TOR-related genes. In addition, hemocytes of abalone were treated with 0, 0.2, 0.5, 1, 2 and 4 mmol/L of arginine, and abalones were fed diets with 1.17%, 1.68% and 3.43% of arginine, respectively, for 120 days. Supplementation of arginine (0.5–4 mmol/L) increased the expressions of slc38a9, tor, s6k and eif4e in hemocytes, and abalone fed with 1.68% of dietary arginine showed higher mRNA levels of slc38a9, tor, s6k and eif4e and phosphorylation levels of TOR, S6 and 4E-BP. In conclusion, the TOR signaling pathway of abalone can be regulated by arginine, and SLC38A9 plays an essential role in this regulation.