Plant heterotrimeric G protein function: insights from Arabidopsis and rice mutants

Heterotrimeric G proteins have been implicated in a wide range of plant processes. These include responses to hormones, drought, and pathogens, and developmental events such as lateral root formation, hypocotyl elongation, hook opening, leaf expansion, and silique development. Results and concepts emerging from recent phenotypic analyses of G-protein component mutants in Arabidopsis and rice are adding to our understanding of G-protein mechanisms and functions in higher plants.     

Defense Responses in Two Ecotypes of Lotus japonicus against Non-Pathogenic Pseudomonas syringae

Lotus japonicus is a model legume broadly used to study many important processes as nitrogen fixing nodule formation and adaptation to salt stress. However, no studies on the defense responses occurring in this species against invading microorganisms have been carried out at the present. Understanding how this model plant protects itself against pathogens will certainly help to develop more tolerant cultivars in economically important Lotus species as well as in other legumes. In order to uncover the most important defense mechanisms activated upon bacterial attack, we explored in this work the main responses occurring in the phenotypically contrasting ecotypes MG-20 and Gifu B-129 of L. japonicus after inoculation with Pseudomonas syringae DC3000 pv. tomato. Our analysis demonstrated that this bacterial strain is unable to cause disease in these accessions, even though the defense mechanisms triggered in these ecotypes might differ. Thus, disease tolerance in MG-20 was characterized by bacterial multiplication, chlorosis and desiccation at the infiltrated tissues. In turn, Gifu B-129 plants did not show any symptom at all and were completely successful in restricting bacterial growth. We performed a microarray based analysis of these responses and determined the regulation of several genes that could play important roles in plant defense. Interestingly, we were also able to identify a set of defense genes with a relative high expression in Gifu B-129 plants under non-stress conditions, what could explain its higher tolerance. The participation of these genes in plant defense is discussed. Our results position the L. japonicus-P. syringae interaction as a interesting model to study defense mechanisms in legume species.     

VOCs-mediated hormonal signaling and crosstalk with plant growth promoting microbes

In the natural environment, plants communicate with various microorganisms (pathogenic or beneficial) and exhibit differential responses. In recent years, research on microbial volatile compounds (MVCs) has revealed them to be simple, effective and efficient groups of compounds that modulate plant growth and developmental processes. They also interfere with the signaling process. Different MVCs have been shown to promote plant growth via improved photosynthesis rates, increased plant resistance to pathogens, activated phytohormone signaling pathways, or, in some cases, inhibit plant growth, leading to death. Regardless of these exhibited roles, the molecules responsible, the underlying mechanisms, and induced specific metabolic/molecular changes are not fully understood. Here, we review current knowledge on the effects of MVCs on plants, with particular emphasis on their modulation of the salicylic acid, jasmonic acid/ethylene, and auxin signaling pathways. Additionally, opportunities for further research and potential practical applications presented.     

PSKR1 and PSY1R-mediated regulation of plant defense responses

Plant peptide signaling is an upcoming topic in many areas of plant research. Our recent findings show that the tyrosine sulfated peptide receptors PSKR1 and PSY1R are not only involved in growth and development but also in plant defense. They modulate salicylate- and jasmonate-dependent defense pathways in an antagonistic manner and this phenomenon might be dependent on the age and developmental stage of the plant. Here we discuss how the endogenous peptides might integrate growth, wounding, senescence and the opposing defense pathways against biotrophic and necrotrophic pathogens for increased fitness of the plant.     

Auxin-oxylipin crosstalk: relationship of antagonists

Stephan Pollmann (Corresponding author) Phytohormones regulate a wide array of developmental processes throughout the life cycle of plants. Herein, the various plant hormones may interact additively, synergistically, or antagonistically. By their cooperation they create a delicate regulatory network whose net output largely depends on the action of specific phytohormone combinations rather than on the independent activities of separate hormones. While most classical studies of plant hormonal control have focused mainly on the action of single hormones or on the synergistic interaction of hormones in regulating various developmental processes, recent work is beginning to shed light on the crosstalk of nominally antagonistic plant hormones, such as gibberellins and auxins with oxylipins or abscisic acid. In this review, we summarize our current understanding of how two of the first sight antagonistic plant hormones, i.e. auxins and oxylipins, interact in controlling plant responses and development.     

植物中逆境反应相关的WRKY转录因子研究进展

WRKY转录因子是植物体内一类比较大的转录因子家族,它在植物的生长发育以及抗逆境反应中起着非常重要的作用。本文综述了WRKY转录因子在植物应对冻害、干旱、盐害等非生物胁迫与病原菌、虫害等生物胁迫反应中的重要调控功能,并概括了WRKY转录因子在调控这些逆境反应中的机制。     

The interplay between light and jasmonate signalling during defence and development

During their evolution, plants have acquired diverse capabilities to sense their environment and modify their growth and development as required. The versatile utilization of solar radiation for photosynthesis as well as a signal to coordinate developmental responses to the environment is an excellent example of such a capability. Specific light quality inputs are converted to developmental outputs mainly through hormonal signalling pathways. Accordingly, extensive interactions between light and the signalling pathways of every known plant hormone have been uncovered in recent years. One such interaction that has received recent attention and forms the focus of this review occurs between light and the signalling pathway of the jasmonate hormone with roles in regulating plant defence and development. Here the recent research that revealed new mechanistic insights into how plants might integrate light and jasmonate signals to modify their growth and development, especially when defending themselves from either pests, pathogens, or encroaching neighbours, is discussed.     

Flavonoids and auxin transport: modulators or regulators?

Flavonoids are polyphenolic compounds found in all vascular and non-vascular plants. Although nonessential for plant growth and development, flavonoids have species-specific roles in nodulation, fertility, defense and UV protection. Flavonoids have been shown to modulate transport of the phytohormone auxin in addition to auxin-dependent tropic responses. However, flavonoids are not essential regulators of these processes because transport and tropic responses occur in their absence. Flavonoids modulate the activity of auxin-transporting P-glycoproteins and seem to modulate the activity of regulatory proteins such as phosphatases and kinases. Phylogenetic analysis suggests that auxin transport mechanisms evolved in the presence of flavonoid compounds produced for the scavenging of reactive oxygen species and defense from herbivores and pathogens.     

Strategies used by bacterial pathogens to suppress plant defenses

Plant immune systems effectively prevent infections caused by the majority of microbial pathogens that are encountered by plants. However, successful pathogens have evolved specialized strategies to suppress plant defense responses and induce disease susceptibility in otherwise resistant hosts. Recent advances reveal that phytopathogenic bacteria use type III effector proteins, toxins, and other factors to inhibit host defenses. Host processes that are targeted by bacteria include programmed cell death, cell wall-based defense, hormone signaling, the expression of defense genes, and other basal defenses. The discovery of plant defenses that are vulnerable to pathogen attack has provided new insights into mechanisms that are essential for both bacterial pathogenesis and plant disease resistance.     

植物免疫应答过程中 Ca2 ＋及 CaM/CML 的功能

钙离子是一个多功能的第二信使,在植物响应各种生理刺激时,Ca2＋参与调节植物的多种生长发育和胁迫适应过程。在这些过程中,Ca2＋信号带有特异性标签,通过Ca2＋结合蛋白及其下游靶蛋白感知不同刺激并翻译成响应的细胞反应。钙调素（CaM）和钙调素类蛋白（CML）是Ca2＋主要感受器,通过调节不同靶蛋白的活性调控多种细胞功能。最近在植物对抗病原菌的防卫反应中有关Ca2＋／CaM信号转导系统的研究取得了一定进展。重点关注植物免疫应答过程中受CaM／CML调控的信号组分的研究,包括参与Ca2＋信号产生和Ca2＋依赖的表达基因组分调控。     

Plant interactions with microbes and insects: from molecular mechanisms to ecology

Plants are members of complex communities and interact both with antagonists and beneficial organisms. An important question in plant defense-signaling research is how plants integrate signals induced by pathogens, beneficial microbes and insects into the most appropriate adaptive response. Molecular and genomic tools are now being used to uncover the complexity of the induced defense signaling networks that have evolved during the arms races between plants and their attackers. Molecular biologists and ecologists are joining forces to place molecular mechanisms of plant defense into an ecological perspective. Here, we review our current understanding of the molecular mechanisms of induced plant defense and their potential ecological relevance in nature.     

Modulation of host immunity by beneficial microbes

In nature, plants abundantly form beneficial associations with soilborne microbes that are important for plant survival and, as such, affect plant biodiversity and ecosystem functioning. Classical examples of symbiotic microbes are mycorrhizal fungi that aid in the uptake of water and minerals, and Rhizobium bacteria that fix atmospheric nitrogen for the plant. Several other types of beneficial soilborne microbes, such as plant-growth-promoting rhizobacteria and fungi with biological control activity, can stimulate plant growth by directly suppressing deleterious soilborne pathogens or by priming aboveground plant parts for enhanced defense against foliar pathogens or insect herbivores. The establishment of beneficial associations requires mutual recognition and substantial coordination of plant and microbial responses. A growing body of evidence suggests that beneficial microbes are initially recognized as potential invaders, after which an immune response is triggered, whereas, at later stages of the interaction, mutualists are able to short-circuit plant defense responses to enable successful colonization of host roots. Here, we review our current understanding of how symbiotic and nonsymbiotic beneficial soil microbes modulate the plant immune system and discuss the role of local and systemic defense responses in establishing the delicate balance between the two partners.     

Defense on multiple fronts: how do plants cope with diverse enemies?

Plants have evolved an array of defense mechanisms to protect themselves against the wide variety of pathogens and pests with which they are confronted. Included in these defense mechanisms are inducible responses that are turned on systemically in the plant in response to attempted infection or predation. The two most studied inducible responses are systemic acquired resistance, which provides enhanced resistance to pathogen infection, and the wound response pathway, resulting in enhanced resistance to insect feeding. Recent research suggests that the two pathways are not completely independent, and the induction of one might affect the expression of the other. However, the evidence for cross-talk between different induced defense response pathways is somewhat confusing, and at times contradictory. Here, we review recent advances in our understanding of how the different pathways might interact.     

Role of pathogen's effectors in understanding host-pathogen interaction

Pathogens can pose challenges to plant growth and development at various stages of their life cycle. Two interconnected defense strategies prevent the growth of pathogens in plants, i.e., molecular patterns triggered immunity (PTI) and pathogenic effector-triggered immunity (ETI) that often provides resistance when PTI no longer functions as a result of pathogenic effectors. Plants may trigger an ETI defense response by directly or indirectly detecting pathogen effectors via their resistance proteins. A typical resistance protein is a nucleotide-binding receptor with leucine-rich sequences (NLRs) that undergo structural changes as they recognize their effectors and form associations with other NLRs. As a result of dimerization or oligomerization, downstream components activate “helper” NLRs, resulting in a response to ETI. It was thought that ETI is highly dependent on PTI. However, recent studies have found that ETI and PTI have symbiotic crosstalk, and both work together to create a robust system of plant defense. In this article, we have summarized the recent advances in understanding the plant's early immune response, its components, and how they cooperate in innate defense mechanisms. Moreover, we have provided the current perspective on engineering strategies for crop protection based on up-to-date knowledge.     

Plant Immunity Induced by Oligogalacturonides Alters Root Growth in a Process Involving Flavonoid Accumulation in Arabidopsis thaliana

Plants adapt to challenging environmental factors by modulating morphogenetic processes. Although it has been speculated that activation of defense responses against pathogens leads to plant growth adjustment, little is known about developmental and architectural responses to defense stimulators. In this report we evaluated the activity of oligogalacturonides (OGs), a class of molecules directly involved in plant immunity, to modulate root system architecture in Arabidopsis thaliana. We show that OGs induce PAD3 expression and camalexin synthesis, two well-known markers of defense responses. These effects were related to primary root growth inhibition and increased lateral root and root hair formation, which are reminiscent of altered auxin responses. Cellular analysis showed that the effect of these compounds on primary root growth was due to changes in cell elongation and increased flavonoid accumulation at the root elongation region. Moreover, the observations that similar changes in primary root growth were induced by naphthylphthalamic acid supply and that auxin- or flavonoid-related mutants tir1, doc1, pgp1, pgp4, pgp19, and tt4-1 show differential responses to primary root growth inhibition by OGs suggest that auxin homeostasis plays a role in the oligogalacturonide-induced alteration of root cell patterning. Our results suggest that OGs might play a dual function in adaptation of plants to pathogen challenge by inducing defense responses and plant architecture adjustment.     

次生代谢产物与植物抗病防御反应

次生代谢产物是由植物次生代谢产生的许多结构不同的小分子有机化合物,它们广泛参与植物的生长、发育、防御等生理过程。次生代谢产物在植物的抗病防御反应中发挥着重要作用,可以作为生化壁垒防御病原物侵染,还可以作为信号物质参与植物的抗病反应;在植物与病原物互作中,植物合成新的抗菌物质植保素,原有的抗菌物质也会增加。植物次生代谢产物的积累受到病原物、发育,环境等多种因素的调节。本文重点介绍次生代谢产物在植物抗病防御中的相关作用以及影响其合成的各种因素。     

Salt Stress Perception and Plant Growth Regulators in the Halophyte Mesembryanthemum crystallinum

We selected indicators of four different metabolic processes (Crassulacean acid metabolism [CAM], amino acid and nitrogen mobilization metabolism, osmoprotection, and plant defense mechanisms) to study the relationship between salt-stress-mediated and plant growth regulator (PGR)-induced responses in Mesembryanthemum crystallinum (ice plant). Nacl and PGRs (cytokinin and abscisic acid [ABA]) are efficient elicitors of the well-studied Nacl stress responses: induction of the CAM form of phosphoenolpyruvate carboxylase, proline pinitol accumulation, and the increase of an osmotin-like protein. NaCl and cytokinin are more effective than ABA in stimulating accumulation of proline and an osmotin-like protein before the plants are committed to flowering. The results are consistent with a plant defense-induction model, in which environmental stress and PGRs are distinct signals whose subsequent effects lead to overlapping responses, the magnitude of which depends on plant developmental status.     

植物microRNAs研究进展

植物microRNAs(miRNAs)是一类与RNA诱导沉默复合体相关的约由22个核苷酸组成的单链小RNA分子, 其主要功能是, 通过特异性剪切靶mRNA或阻遏靶mRNA的正常翻译在转录后水平调控基因的负表达。植物miRNAs的靶标主要是参与调控植物生长发育和防御应答的转录因子家族。文章主要综述miRNAs在植物体内的生物发生、作用机制及其调控作用研究新进展。