Source-sink regulation by sugar and stress.

The regulation of carbon partitioning between source and sink tissues in higher plants is not only important for plant growth and development, but insight into the underlying regulatory mechanism is also a prerequisite to modulating assimilate partitioning in transgenic plants. Hexoses, as well as sucrose, have been recognised as important signal molecules in source-sink regulation. Components of the underlying signal transduction pathways have been identified and parallels, as well as distinct differences, to known pathways in yeast and animals have become apparent. There is accumulating evidence for crosstalk, modulation and integration between signalling pathways responding to phytohormones, phosphate, light, sugars, and biotic and abiotic stress-related stimuli. These complex interactions at the signal transduction levels and co-ordinated regulation of gene expression seem to play a central role in source-sink regulation.     

Emerging MAP kinase pathways in plant stress signalling

Mitogen-activated protein kinase (MAPK) pathways transfer information from sensors to cellular responses in all eukaryotes. A surprisingly large number of genes encoding MAPK pathway components have been uncovered by analysing model plant genomes, suggesting that MAPK cascades are abundant players of signal transduction. Recent investigations have confirmed major roles of defined MAPK pathways in development, cell proliferation and hormone physiology, as well as in biotic and abiotic stress signalling. Latest insights and findings are discussed in the context of novel MAPK pathways in plant stress signalling.     

Salicylic acid-independent plant defence pathways

Salicylic acid is an important signalling molecule involved in both locally and systemically induced disease resistance responses. Recent advances in our understanding of plant defence signalling have revealed that plants employ a network of signal transduction pathways, some of which are independent of salicylic acid. Evidence is emerging that jasmonic acid and ethylene play key roles in these salicylic acid-independent pathways. Cross-talk between the salicylic acid-dependent and the salicylic acid-independent pathways provides great regulatory potential for activating multiple resistance mechanisms in varying combinations.     

Tête-à-tête: the function of FKBPs in plant development

Compared with that of other eukaryotes, the nuclear genome of the model plant Arabidopsis thaliana encodes an expanded family of FK506-binding proteins (FKBPs). Whereas approximately half of the FKBPs are implicated in the regulation of photosynthetic processes, a subcluster appears to be stress responsive. Recent reports indicate that a discrete group of Arabidopsis multidomain FKBPs regulate plant hormone pathways by recruiting or modulating client proteins via direct protein-protein interactions (tête-à-tête). This suggests that multidomain FKBPs function as central elements in plant development by linking hormone responses with other signal transduction pathways. Here, we present a summary of current research demonstrating that, in addition to their role in protein folding, subsets of plant FKBPs exhibit diverse functionality.     

Degradation of negative regulators: a common theme in hormone and light signaling networks?

Signal transduction pathways often modulate both positively and negatively acting components to optimize the efficiency of a signal. Recent results have shown that plants make extensive use of regulated proteolysis to modulate signal transduction pathways. An emerging theme from hormone (e.g. auxin and gibberellin) and light signaling pathways is signal or stimulus-induced degradation of negative regulators to optimize plant growth and development.     

Structural and functional diversity of adaptor proteins involved in tyrosine kinase signalling

Adaptors are proteins of multi-modular structure without enzymatic activity. Their capacity to organise large, temporary protein complexes by linking proteins together in a regulated and selective fashion makes them of outstanding importance in the establishment and maintenance of specificity and efficiency in all known signal transduction pathways. This review focuses on the structural and functional characterisation of adaptors involved in tyrosine kinase (TK) signalling. TK-linked adaptors can be distinguished by their domain composition and binding specificities. However, such structural classifications have proven inadequate as indicators of functional roles. A better way to understand the logic of signalling networks might be to look at functional aspects of adaptor proteins such as signalling specificity, negative versus positive contribution to signal propagation, or their position in the signalling hierarchy. All of these functions are dynamic, suggesting that adaptors have important regulatory roles rather than acting only as stable linkers in signal transduction.     

Sugars as signaling molecules.

Recent studies indicate that, in a manner similar to classical plant hormones, sugars can act as signaling molecules that control gene expression and developmental processes in plants. Crucial evidence includes uncoupling glucose signaling from its metabolism, identification of glucose sensors, and isolation and characterization of mutants and other regulatory components in plant sugar signal transduction pathways. The emerging scenario points to the existence of a complex signaling network that interconnects transduction pathways from sugars and other hormone and nutrient signals.     

植物中的核质转运相关蛋白

细胞内各个生命过程的有序进行需要生物大分子在细胞核与细胞质之间有选择、有控制地转运.而细胞核膜的存在为大分子的自由穿梭设置了屏障,因此生物大分子在细胞核与细胞质之间的转运要依赖于一些受体蛋白.输入蛋白β(importinβ)是首先从人类细胞中发现的生物大分子向细胞核输入的受体,其后相继鉴定出多个与输入蛋白β具有同源性的细胞核转运受体,命名为类输入蛋白β.这些转运受体介导的转运过程在生物有机体之间高度保守,在动物及酵母中调控核质穿梭以及各个信号过程的组分与分子机制研究较为清楚,但在植物中相对匮乏.本文在介绍细胞核转运受体共有结构特点和转运机制基础上,重点综述了植物细胞核转运受体的最新研究进展以及这些受体在植物信号转导中的重要调节作用.     

玉米性别决定的激素调控

玉米(Zea mays)属典型的雌雄异花植物, 单性花的形成经历了复杂的性别决定过程。通过雄穗小花和雌穗下位花的雌蕊原基以及雌穗小花雄蕊原基的选择性败育(或退化), 玉米最终形成正常的雌雄同株单性花。相关突变体的研究揭示, 玉米性别决定涉及选择性细胞死亡、细胞保护及信号转导等复杂的过程。其中, 植物激素信号的调控在玉米性别决定过程中处于核心地位。最近的研究表明, 赤霉素、细胞分裂素和茉莉酸类物质参与调控玉米性别决定过程。该文结合最新研究成果, 综述了植物激素在玉米性别决定中的作用及其调控途径, 同时提出了研究中存在的问题, 并对该领域未来的研究方向进行了展望。     

Receptors and signalling components of plant hormones

Recent advances in understanding plant hormonal signalling has resulted in the identification of a variety of signalling components including receptor kinases with homology to the bacterial two component system as well as serine/threonine kinases and protein phosphatases. In addition, the existence of MAP kinase pathways in plants indicates a similar role of these signalling cascades in the relay of exogenous signals into the nucleus as has been disclosed in animal cells. The emerging signalling pathways of the plant hormone abscisic acid and ethylene are presented.     

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.     

Protein complexes mediate signalling in plant responses to hormones,light, sucrose and pathogens

Living organisms use complex pathways of signal perception and transduction to respond to stimuli in their environments. In plants, putative signal transduction components have been identified through mutant screens and comparative analysis of genome sequences of model eukaryotes. Several pieces in a large series of puzzles have now been identified and a current challenge is to determine how these pieces interconnect. Functional analysis of the encoded proteins has necessitated a change from genetic to biochemical approaches. In recent years, the application of techniques such as two-hybrid screening and epitope tagging has facilitated the study of protein-protein interactions and has increased our understanding of cellular signalling mechanisms. One focus of present research is the ubiquitin/proteasome-mediated degradation of proteins. Increasing evidence suggests this is a control common to many plant signalling pathways including development and responsiveness to hormones, light and sucrose. A central challenge in the study of plant disease resistance has been to identify protein complexes that contain host defence proteins and pathogenicity factors. In this review we summarize the latest developments in these areas where the existence of protein complexes has been demonstrated to be of fundamental importance in plant signalling.     

Signal transduction in response to excess light: getting out of the chloroplast.

Plants are continually in danger of absorbing more light energy than they can use productively for their metabolism. Acclimation to environmental conditions therefore includes the development of mechanisms for dissipating or avoiding the accumulation of such excess excitation energy. Acclimation could be controlled by many signal transduction pathways that would be initiated by the perception of excess excitation energy both inside and outside the chloroplast. Recent studies in related areas provide models of how these signalling pathways could operate in acclimation to excess light. Components of photosynthetic electron transport chains, reactive oxygen species, redox-responsive protein kinases, thiol-regulated enzymes, chlorophyll precursors and chloroplast-envelope electron transport chains all have roles in these models.