The Role of Selective Protein Degradation in the Regulation of Iron and Sulfur Homeostasis in Plants

Plants are able to synthesize all essential metabolites from minerals, water, and light to complete their life cycle. This plasticity comes at a high energy cost, and therefore, plants need to tightly allocate resources in order to control their economy. Being sessile, plants can only adapt to fluctuating environmental conditions, relying on quality control mechanisms. The remodeling of cellular components plays a crucial role, not only in response to stress, but also in normal plant development. Dynamic protein turnover is ensured through regulated protein synthesis and degradation processes. To e�ectively target a wide range of proteins for degradation, plants utilize two mechanistically-distinct, but largely complementary systems: the 26S proteasome and the autophagy. As both proteasomaland autophagy-mediated protein degradation use ubiquitin as an essential signal of substrate recognition, they share ubiquitin conjugation machinery and downstream ubiquitin recognition modules. Recent progress has been made in understanding the cellular homeostasis of iron and sulfur metabolisms individually, and growing evidence indicates that complex crosstalk exists between iron and sulfur networks. In this review, we highlight the latest publications elucidating the role of selective protein degradation in the control of iron and sulfur metabolism during plant development, as well as environmental stresses

Proteasomal Degradation of Proteins is Important for the Proper Transcriptional Response to Sulfur Deficiency Conditions in Plants

Plants are continuously exposed to different abiotic and biotic stresses; therefore, to protect themselves they depend on the fast reprogramming of large gene repertoires to prioritize the expression of a given stress-induced gene set over normal cellular household genes. The activity of the proteasome, a large proteolytic complex that degrades proteins, is vital to coordinate the expression of such genes. Proteins are labeled for degradation by the action of E3 ligases that site-specifically alter their substrates by adding chains of ubiquitin. Recent publications have revealed an extensive role of ubiquitination in nutrients utilization. This study presents the transcriptomic profiles of sulfur-deficient rosettes and roots of Arabidopsis thaliana rpt2a mutant with proteasomal malfunction. We found that genes connected with sulfur metabolism are regulated to the lesser extent in rpt2a mutant while genes encoding tRNAs and snoRNAs are highly upregulated. Several genes encoding E3 ligases are specifically regulated by sulfur deficiency. Furthermore, we show that a key transcription factor of sulfur deficiency response, SLIM1, undergoes proteasomal degradation and is able to interact with F-box protein, EBF1

EIN3 interferes with the sulfur deficiency signaling in Arabidopsis thaliana through direct interaction with the SLIM1 transcription factor

tSulfur deficiency in plants leads to metabolic reprogramming through changes of gene expression. SLIM1is so far the only characterized transcription factor associated strictly with sulfur deficiency stress inArabidopsis thaliana. It belongs to the same protein family as EIN3, a major positive switch of ethylenesignaling pathway. It binds to the specific cis sequence called UPE-box. Here we show that SLIM1 interactswith UPE-box as a homodimer. Interestingly, the same region of the protein is used for heterodimerizationwith EIN3; however, the heterodimer is not able to recognize UPE-box. Expression of several SLIM1-dependent genes is enhanced in sulfur deficiency grown Arabidopsis ein3-1 seedlings (with mutatedEIN3 protein). This implies a possible regulatory mechanism of ethylene in sulfur metabolism throughdirect EIN3-SLIM1 interaction

Similar but Not Identical—Binding Properties of LSU (Response to Low Sulfur) Proteins From Arabidopsis thaliana

Members of the plant-specific LSU (RESPONSE TO LOW SULFUR) family are strongly induced during sulfur starvation. The molecular functions of these proteins are unknown; however, they were identified as important stress-related hubs in several studies. In Arabidopsis thaliana, there are four members of the LSU family (LSU1–4). These proteins are small (approximately 100 amino acids), with coiled-coil structures. In this work, we investigated interactions between different monomers of LSU1–4. Differences in homo and heterodimer formation were observed. Our structural models of LSU1–4 homo- and heterodimers were in agreement with our experimental observations and may help understand their binding properties. LSU proteins are involved in multiple protein–protein interactions, with the literature suggesting they can integrate abiotic and biotic stress responses. Previously, LSU partners were identified using the yeast two hybrid approach, therefore we sought to determine proteins co-purifying with LSU family members using protein extracts isolated from plants ectopically expressing TAP-tagged LSU1–4 constructs. These experiments revealed 46 new candidates for LSU partners. We tested four of them (and two other proteins, CAT2 and NBR1) for interaction with LSU1–4 by other methods. Binding of all six proteins with LSU1–4 was confirmed by Bimolecular Fluorescence Complementation, while only three of them were interacting with LSUs in yeast-two-hybrid. Additionally, we conducted network analysis of LSU interactome and revealed novel clues for the possible cellular function of these proteins

Editorial: Protein posttranslational modifications in plant responses to abiotic stress - Women in plant science series

Peer reviewe

Control of ABA Signaling and Crosstalk with Other Hormones by the Selective Degradation of Pathway Components

A rapid and appropriate genetic and metabolic acclimation, which is crucial for plants’survival in a changing environment, is maintained due to the coordinated action of plant hormones and cellular degradation mechanisms influencing proteostasis. The plant hormone abscisic acid (ABA) rapidly accumulates in plants in response to environmental stress and plays a pivotal role in the reaction to various stimuli. Increasing evidence demonstrates a significant role of autophagy in controlling ABA signaling. This field has been extensively investigated and new discoveries are constantly being provided. We present updated information on the components of the ABA signaling pathway, particularly on transcription factors modified by different E3 ligases. Then, we focus on the role of selective autophagy in ABA pathway control and review novel evidence on the involvement of autophagy in different parts of the ABA signaling pathway that are important for crosstalk with other hormones, particularly cytokinins and brassinosteroids

Acquired methemoglobinemia - case report

Methemoglobinemia jest rzadko rozpoznawaną, groźną dla życia patologią polegającą na obecności we krwi ponad 1% utlenionej hemoglobiny, która jest niezdolna do przenoszenia tlenu. Przypadek dotyczy 49-letniego mężczyzny z gwałtownie narastającymi objawami ostrej, hipoksemicznej niewydolności oddechowej, u którego wykluczono ostre i przewlekłe choroby układów krążenia i oddechowego. Istotna rozbieżność pomiędzy wartością saturacji tlenem, odczytanej z pulsoksymetru, a saturacją tlenem oraz ciśnieniem parcjalnym tlenu, obliczonymi w badaniu gazometrycznym krwi włośniczkowej, a także wyraźny brak reakcji na tlenoterapię były ważnymi wskazówkami do poszukiwania hemoglobinopatii i rozpoznania methemoglobinemii. Stężenie methemoglobiny wynosiło 16%. Objawy ustąpiły samoistnie. Czynnik wywołujący methemoglobinemię nie został zidentyfikowany. Pneumonol. Alergol. Pol. 2010; 78, 2: 153-158Methemoglobinemia; an increased concentration of methemoglobin in the blood, is an altered state of hemoglobin whereby the ferrous form of iron is oxidized to the ferric state, rendering the heme moiety incapable of carrying oxygen. The authors present a case of 49-year-old man who was admitted to the department of chest medicine with dyspnea, weakness and cyanosis in whom differential diagnosis excluded acute and chronic pulmonary and cardiovascular disease. Clinical cyanosis and low measured oxygen saturation in the presence of normal arterial oxygen tension was highly suggestive of methemoglobinemia ("saturation gap"). Methemoglobin level, measured at the acute phase of disease was elevated at 16%. Episode resolved spontaneously. Causes of methemoglobinemia was not established. Pneumonol. Alergol. Pol. 2010; 78, 2: 153-15

The SLIM1 transcription factor affects sugar signaling during sulfur deficiency in Arabidopsis

The homeostasis of major macronutrient metabolism needs to be tightly regulated, especially when the availability of one or more nutrients fluctuates in the environment. Both sulfur metabolism and glucose signaling are important processes throughout plant growth and development, as well as during stress responses. Still, very little is known about how these processes affect each other, although they are positively connected. Here, we showed in Arabidopsis that the crucial transcription factor of sulfur metabolism, SLIM1, is involved in glucose signaling during shortage of sulfur. The germination rate of the slim1_KO mutant was severely affected by high glucose and osmotic stress. The expression of SLIM1-dependent genes in sulfur deficiency appeared to be additionally induced by a high concentration of either mannitol or glucose, but also by sucrose, which is not only the source of glucose but another signaling molecule. Additionally, SLIM1 affects PAP1 expression during sulfur deficiency by directly binding to its promoter. The lack of PAP1 induction in such conditions leads to much lower anthocyanin production. Taken together, our results indicate that SLIM1 is involved in the glucose response by modulating sulfur metabolism and directly controlling PAP1 expression in Arabidopsis during sulfur deficiency stress