The impact of high-temperature stress on rice: Challenges and solutions

Heat stress (HS) caused by rapidly warming climate has become a serious threat to global food security.Rice (Oryza sativa L.) is a staple food crop for over half of the world’s population,and its yield and quality are often reduced by HS.There is an urgent need for breeding heat-tolerant rice cultivars.Rice plants show various morphological and physiological symptoms under HS.Precise analysis of the symptoms(phenotyping) is essential for the selection of elite germplasm and the identification of thermotolerance genes.In response to HS,rice plants trigger a cascade of events and activate complex transcriptional regulatory networks.Protein homeostasis under HS is especially important for rice thermotolerance,which is affected by protein quality control,effective elimination of toxic proteins,and translational regulation.Although some agronomic and genetic approaches for improving heat tolerance have been adopted in rice,the molecular mechanisms underlying rice response to HS are still elusive,and success in engineering rice thermotolerance in breeding has been limited.In this review,we summarize HS-caused symptoms in rice and progress in heat-stress sensing and signal cascade research,and propose approaches for improving rice thermotolerance in future.

Regulation of chloroplast protein degradation

Chloroplasts are unique organelles that not only provide sites for photosynthesis and many metabolic processes,but also are sensitive to various environmental stresses.Chloroplast proteins are encoded by genes from both nuclear and chloroplast genomes.During chloroplast development and responses to stresses,the robust protein quality control systems are essential for regulation of protein homeostasis and the integrity of chloroplast proteome.In this review,we summarize the regulatory mechanisms of chloroplast protein degradation refer to protease system,ubiquitin-proteasome system,and the chloroplast autophagy.These mechanisms symbiotically play a vital role in chloroplast development and photosynthesis under both normal or stress conditions.

eIF-Three to Tango: emerging functions of translation initiation factor eIF3 in protein synthesis and disease

Studies over the past three years have substantially expanded the involvements of eukaryotic initiation factor 3 (eIF3) in messenger RNA (mRNA) translation. It now appears that this multi-subunit complex is involved in every possible form of mRNA translation, controlling every step of protein synthesis from initiation to elongation, termination, and quality control in positive as well as negative fashion. Through the study of eIF3, we are beginning to appreciate protein synthesis as a highly integrated process coordinating protein production with protein folding, subcellular targeting, and degradation. At the same time, eIF3 subunits appear to have specific functions that probably vary between different tissues and individual cells. Considering the broad functions of eIF3 in protein homeostasis, it comes as little surprise that eIF3 is increasingly implicated in major human diseases and first attempts at therapeutically targeting eIF3 have been undertaken. Much remains to be learned, however, about subunit- and tissue-specific functions of eIF3 in protein synthesis and disease and their regulation by environmental conditions and post-translational modifications.

Essentials of Proteolytic Machineries in Chloroplasts

Plastids are unique organelles that can alter their structure and function in response to environmental and developmental stimuli. Chloroplasts are one type of plastid and are the sites for various metabolic pro- cesses, including photosynthesis. For optimal photosynthetic activity, the chloroplast proteome must be properly shaped and maintained through regulated proteolysis and protein quality control mechanisms. Enzymatic functions and activities are conferred by protein maturation processes involving consecutive proteolytic reactions. Protein abundances are optimized by the balanced protein synthesis and degrada- tion, which is depending on the metabolic status. Malfunctioning proteins are promptly degraded. Twenty chloroplast proteolytic machineries have been characterized to date. Specifically, processing peptidases and energy-driven processive proteases are the major players in chloroplast proteome biogenesis, remod- eling, and maintenance. Recently identified putative proteases are potential regulators of photosynthetic functions. Here we provide an updated, comprehensive overview of chloroplast protein degradation ma- chineries and discuss their importance for photosynthesis. Wherever possible, we also provide structural insights into chloroplast proteases that implement regulated proteolysis of substrate proteins/peptides.

Caenorhabditis elegans homologue of Fam210 is required for oogenesis and reproduction

Mitochondria are the central hub for many metabolic processes,including the citric acid cycle,oxidative phosphorylation,and fatty acid oxidation.Recent studies have identified a new mitochondrial protein family,Fam210,that regulates bone metabolism and red cell development in vertebrates.The model organism Caenorhabditis elegans has a Fam210 gene,y56a3a.22,but it lacks both bones and red blood cells.In this study,we report that Y56A3A.22 plays a crucial role in regulating mitochondrial protein homeostasis and reproduction.The nematode y56a3a.22 is expressed in various tissues,including the intestine,muscle,hypodermis,and germline,and its encoded protein is predominantly localized in mitochondria.y56a3a.22 deletion mutants are sterile owing to impaired oogenesis.Loss of Y56A3A.22 induced mitochondrial unfolded protein response(UPRmt),which is mediated through the ATFS-1-dependent pathway,in tissues such as the intestine,germline,hypodermis,and vulval muscle.We further show that infertility and UPRmt induces by Y56A3A.22 deficiency are not attributed to systemic iron deficiency.Together,our study reveals an important role of Y56A3A.22 in regulating mitochondrial protein homeostasis and oogenesis and provides a new genetic tool for exploring the mechanisms regulating mitochondrial metabolism and reproduction as well as the fundamental role of the Fam210 family.