Unconventional myosins at the crossroad of signal transduction and cytoskeleton remodeling

Summary The cytoplasm of eukaryotic cells is a complex milieu and unraveling how its unique cytoarchitecture is achieved and maintained is a central theme in modern cell biology. The actin cytoskeleton is essential for the maintenance of cell shape and locomotion, and also provides tracks for active intracellular transport. Myosins, the actin-dependent motor proteins form a superfamily of at least 15 structural classes and have been identified in a wide variety of organisms, making the presence of actin and myosins a hallmark feature of eukaryotes. Direct connections of myosins to a variety of cellular tasks are now emerging, such as in cytokinesis, phagocytosis, endocytosis, polarized secretion and exocytosis, axonal transport. Recent studies reveal that myosins also play an essential role in many aspects of signal transduction and neurosensation.     

Unconventional myosins at the crossroad of signal transduction and cytoskeleton remodeling

The cytoplasm of eukaryotic cells is a complex milieu and unraveling how its unique cytoarchitecture is achieved and maintained is a central theme in modern cell biology. The actin cytoskeleton is essential for the maintenance of cell shape and locomotion, and also provides tracks for active intracellular transport. Myosins, the actin-dependent motor proteins form a superfamily of at least 15 structural classes and have been identified in a wide variety of organisms, making the presence of actin and myosins a hallmark feature of eukaryotes. Direct connections of myosins to a variety of cellular tasks are now emerging, such as in cytokinesis, phagocytosis, endocytosis, polarized secretion and exocytosis, axonal transport. Recent studies reveal that myosins also play an essential role in many aspects of signal transduction and neurosensation.     

ABA signal transduction

Recent advances in the study of abscisic acid signal transduction include the identification of cyclic ADP-ribose as a central mediator of abscisic acid responses. The characterisation of type 2C protein phosphatases, ABI1 and ABI2, implicates negative control and redundant action on the signal pathway of this hormone. In addition, abscisic acid-mediated inhibition of gibberellin-stimulated responses seems to depend on the activation of a phospholipase D during induction of alpha-amylase in barley aleurone cells as well as on a putative acetyltransferase involved in elongation growth.     

Arabidopsis stress associated protein 9 mediates biotic and abiotic stress responsive ABA signaling via the proteasome pathway

Arabidopsis thaliana Stress Associated Protein 9 (AtSAP9) is a member of the A20/AN1 zinc finger protein family known to play important roles in plant stress responses and in the mammalian immune response. Although SAPs of several plant species were shown to be involved in abiotic stress responses, the underlying molecular mechanisms are largely unknown, and little is known about the involvement of SAPs in plant disease responses. Expression of SAP9 in Arabidopsis is up‐regulated in response to dehydration, cold, salinity and abscisic acid (ABA), as well as pathogen infection. Constitutive expression of AtSAP9 in Arabidopsis leads to increased sensitivity to ABA and osmotic stress during germination and post‐germinative development. Plants that overexpress AtSAP9 also showed increased susceptibility to infection by non‐host pathogen Pseudomonas syringae pv. phaseolicola, indicating a potential role of AtSAP9 in disease resistance. AtSAP9 was found to interact with RADIATION SENSITIVE23d (Rad23d), a shuttle factor for the transport of ubiquitinated substrates to the proteasome, and it is co‐localized with Rad23d in the nucleus. Thus, AtSAP9 may promote the protein degradation process by mediating the interaction of ubiquitinated targets with Rad23d. Taken together, these results indicate that AtSAP9 regulates abiotic and biotic stress responses, possibly via the ubiquitination/proteasome pathway.     

Role of miRNAs and siRNAs in biotic and abiotic stress responses of plants

Small, non-coding RNAs are a distinct class of regulatory RNAs in plants and animals that control a variety of biological processes. In plants, several classes of small RNAs with specific sizes and dedicated functions have evolved through a series of pathways. The major classes of small RNAs include microRNAs (miRNAs) and small interfering RNAs (siRNAs), which differ in their biogenesis. miRNAs control the expression of cognate target genes by binding to reverse complementary sequences, resulting in cleavage or translational inhibition of the target RNAs. siRNAs have a similar structure, function, and biogenesis as miRNAs but are derived from long double-stranded RNAs and can often direct DNA methylation at target sequences. Besides their roles in growth and development and maintenance of genome integrity, small RNAs are also important components in plant stress responses. One way in which plants respond to environmental stress is by modifying their gene expression through the activity of small RNAs. Thus, understanding how small RNAs regulate gene expression will enable researchers to explore the role of small RNAs in biotic and abiotic stress responses. This review focuses on the regulatory roles of plant small RNAs in the adaptive response to stresses. This article is part of a Special Issue entitled: Plant gene regulation in response to abiotic stress.     

NAC转录因子在植物抗病和抗非生物胁迫反应中的作用

NAC转录因子是植物特有的一类转录因子,其共同特点是在N端含有一段高度保守、由约150个氨基酸组成的NAC结构域,而C端为高度变异的转录调控区。研究表明,NAC转录因子不仅参与植物生长发育的调控,而且在植物抗逆反应中具有重要的调控作用。文章着重介绍NAC转录因子在植物抗逆反应中的作用及其调控机制,并简要讨论NAC转录因子生物学功能的研究方向。     

The role of ABA and MAPK signaling pathways in plant abiotic stress responses

As sessile organisms, plants have developed specific mechanisms that allow them to rapidly perceive and respond to stresses in the environment. Among the evolutionarily conserved pathways, the ABA (abscisic acid) signaling pathway has been identified as a central regulator of abiotic stress response in plants, triggering major changes in gene expression and adaptive physiological responses. ABA induces protein kinases of the SnRK family to mediate a number of its responses. Recently, MAPK (mitogen activated protein kinase) cascades have also been shown to be implicated in ABA signaling. Therefore, besides discussing the role of ABA in abiotic stress signaling, we will also summarize the evidence for a role of MAPKs in the context of abiotic stress and ABA signaling.     

Resistance to biotic and abiotic stress in the Triticeae

Poverty, hunger and malnutrition occur in many parts of the world despite the enormous progress that has taken place in agriculture and food production in the last century. It is estimated for wheat, that by 2020 the world will require a 60% increase in production to meet the projected requirement. Resistance to both biotic and abiotic stresses will be critical in reaching this goal. Distinct advantages accompany the use of genetic resistance to biotic and abiotic stresses. The most important advantage is the fact that response to the stress situation occurs independently of the managerial ability, skill and resource level of the producer. Anyone can use a stress resistant crop. Immense progress has been made in the field of functional genomics and molecular manipulation. It is clear that the restraining factor in future will not be the availability of scientific techniques and tools, or for that matter, genetic resources; but the human and financial capacity to achieve the goals on a world-wide scale so that they really do make a difference to the livelihood of the poor. Triticeae form a meaningful proportion of staple and non-staple food crops around the world. To achieve world-wide food security in the future, Triticeae with resistance to stresses will have to play a major role. The future demands crops with stable yield irrespective of environmental constraints, good quality and a high nutritional value; crops that are free of pesticide residues and other harmful substances.     

Structural evolution and function of stress associated proteins in regulating biotic and abiotic stress responses in plants

Adverse environmental conditions greatly influence crop production every year and threaten food security. Plants have a range of signaling networks to combat these stresses, in which several stress-responsive genes and regulatory proteins function together. One such important family of proteins, the Stress Associated Protein (SAP) family, has been identified as a novel regulator of multiple stresses. The SAPs possess a characteristic N-terminal A20 zinc-finger domain combined with either AN1 or C₂H₂ at the C-terminus. SAPs provide tolerance against various abiotic stresses, including cold, salt, drought, heavy metal, and wounding. The majority of SAPs are stress-inducible and have a function in conferring stress tolerance in transgenics. The role of SAPs in regulating biotic stress responses is a newly emerging field among researchers. SAPs interact with many other proteins to execute their functions; however, the detailed mechanism of these interactions needs to be elucidated. In this context, the present review provides a detailed view of the evolution and functions of SAPs in plants. The involvement in crosstalk between abiotic and biotic stress signaling pathways makes SAPs ideal targets to develop crops with tolerance against multiple stresses without any yield penalty. Altogether, we provide current knowledge on SAPs for investigating their role in stress response, which can further be exploited to develop climate-resilient crops through transgene-based, breeding-mediated, or genome-editing approaches.

     

ABA signal transduction from ABA receptors to ion channels

The plant hormone abscisic acid (ABA) is involved in regulating a number of major processes such as seed dormancy, seedling development, and biotic and abiotic stress responses. The function and effect of ABA on pathogens are still unclear, but the roles of ABA in seed germination and abiotic stress responses have been well characterized. Abiotic stresses elevate ABA levels and activate ABA signaling; thus, inducing a variety of responses, including the expression of stress-related genes and stomatal closure. The past decade has witnessed many significant advances in our understanding of ABA signal transduction due to application of a combination of approaches including genetics, biochemistry, electrophysiology, and chemical genetics. A number of proteins associated with the ABA signal transduction pathway such as PYR/PYL/RCAR family of START proteins, have been identified. These ABA receptors bind to ABA and positively regulate ABA signaling via inactivation of PP2C phosphatase activity, which inhibits SnRK2-type kinases by direct interaction and dephosphorylation. Additionally, SnRK2-type kinases and PP2Cs interact with one another and with other components of ABA signaling and function as positive and negative ABA regulators, respectively. In this review, we focus on ABA function to abiotic stresses and highlight each component in relation to ABA and its interactions.     

Roles of a membrane-bound caleosin and putative peroxygenase in biotic and abiotic stress responses in Arabidopsis

We report here the localisation and properties of a new membrane-bound isoform of caleosin and its putative role as a peroxygenase involved in oxylipin metabolism during biotic and abiotic stress responses in Arabidopsis. Caleosins are a family of lipid-associated proteins that are ubiquitous in plants and true fungi. Previous research has focused on lipid-body associated, seed-specific caleosins that have peroxygenase activity. Here, we demonstrate that a separate membrane-bound constitutively expressed caleosin isoform (Clo-3) is highly upregulated following exposure to abiotic stresses, such as salt and drought, and to biotic stress such as pathogen infection. The Clo-3 protein binds one atom of calcium per molecule, is phosphorylated in response to stress, and has a similar peroxygenase activity to the seed-specific Clo-1 isoform. Clo-3 is present in microsomal and chloroplast envelope fractions and has a type I membrane orientation with about 2 kDa of the C terminal exposed to the cytosol. Analysis of Arabidopsis ABA and related mutant lines implies that Clo-3 is involved in the generation of oxidised fatty acids in stress related signalling pathways involving both ABA and salicylic acid. We propose that Clo-3 is part of an oxylipin pathway induced by multiple stresses and may also generate fatty acid derived anti-fungal compounds for plant defence.     

Systemin-dependent salinity tolerance in tomato: evidence of specific convergence of abiotic and biotic stress responses

Plants have evolved complex mechanisms to perceive environmental cues and develop appropriate and coordinated responses to abiotic and biotic stresses. Considerable progress has been made towards a better understanding of the molecular mechanisms of plant response to a single stress. However, the existence of cross-tolerance to different stressors has proved to have great relevance in the control and regulation of organismal adaptation. Evidence for the involvement of the signal peptide systemin and jasmonic acid in wound-induced salt stress adaptation in tomato has been provided. To further unravel the functional link between plant responses to salt stress and mechanical damage, transgenic tomato ( Lycopersicon esculentum Mill.) plants constitutively expressing the prosystemin cDNA have been exposed to a moderate salt stress. Prosystemin over-expression caused a reduction in stomatal conductance. However, in response to salt stress, prosystemin transgenic plants maintained a higher stomatal conductance compared with the wild-type control. Leaf concentrations of abscissic acid (ABA) and proline were lower in stressed transgenic plants compared with their wild-type control, implying that either the former perceived a less stressful environment or they adapted more efficiently to it. Consistently, under salt stress, transgenic plants produced a higher biomass, indicating that a constitutive activation of wound responses is advantageous in saline environment. Comparative gene expression profiling of stress-induced genes suggested that the partial stomatal closure was not mediated by ABA and/or components of the ABA signal transduction pathway. Possible cross-talks between genes involved in wounding and osmotic stress adaptation pathways in tomato are discussed.     

Metabolic regulation of leaf senescence: interactions of sugar signalling with biotic and abiotic stress responses

Sugars are important signals in the regulation of plant metabolism and development. During stress and in senescing leaves, sugars often accumulate. In addition, both sugar accumulation and stress can induce leaf senescence. Infection by bacterial and fungal pathogens and attack by herbivores and gall-forming insects may influence leaf senescence via modulation of the sugar status, either by directly affecting primary carbon metabolism or by regulating steady state levels of plant hormones. Many types of biotic interactions involve the induction of extracellular invertase as the key enzyme of an apoplasmic phloem unloading pathway, resulting in a sourcesink transition and an increased hexose/sucrose ratio. Induction of the levels of the phytohormones ethylene and jasmonate in biotic interactions results in accelerated senescence, whereas an increase in plant- or pathogen-derived cytokinins delays senescence and results in the formation of green islands within senescing leaves. Interactions between sugar and hormone signalling also play a role in response to abiotic stress. For example, interactions between sugar and abscisic acid (ABA) signalling may be responsible for the induction of senescence during drought stress. Cold treatment, on the other hand, can result in delayed senescence, despite sugar and ABA accumulation. Moreover, natural variation can be found in senescence regulation by sugars and in response to stress: in response to drought stress, both drought escape and dehydration avoidance strategies have been described in different Arabidopsis accessions. The regulation of senescence by sugars may be key to these different strategies in response to stress.     

植物蛋白激酶介导的非生物胁迫和激素信号转导途径的研究进展

干旱、盐渍、低温和高温等非生物胁迫严重影响植物的生长发育和作物的产量。在长期的进化过程中,植物逐渐形成了对外部刺激快速感知和主动适应的能力,其中植物体内逆境信号的传递在植物快速感知外部刺激和主动适应非生物胁迫过程中起着非常重要的作用。蛋白激酶和蛋白磷酸酶催化的蛋白质磷酸化和去磷酸化是植物体内存在的最普遍且最重要的信号转导调节方式。其中,蛋白激酶的主要作用是将ATP或GTP上的γ磷酸基团转移到特定的底物蛋白上,使蛋白磷酸化,被磷酸化的蛋白发挥相应的生理功能。近年来,利用生物技术和基因工程等手段从细胞、分子水平上研究有关蛋白激酶的抗逆机理,通过基因沉默、基因过表达等策略提高植物的抗逆性成为国内外抗逆分子生物学与分子育种学研究的热点。本文主要对植物蛋白激酶在介导非生物胁迫和激素信号通路中的作用进行综述,为进一步研究植物蛋白激酶功能提供有价值的信息。