抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Rapid improvements in sequencing and array-based platforms are resulting in a flood of diverse genome-wide data, including data from exome and whole-genome sequencing, epigenetic surveys, expression profiling of coding and noncoding RNAs, single nucleotide polymorphism (SNP) and copy number profiling, and functional assays. Analysis of these large, diverse data sets holds the promise of a more comprehensive understanding of the genome and its relation to human disease. Experienced and knowledgeable human review is an essential component of this process, complementing computational approaches. This calls for efficient and intuitive visualization tools able to scale to very large data sets and to flexibly integrate multiple data types, including clinical data. However, the sheer volume and scope of data pose a significant challenge to the development of such tools.

Integrative Genomics Viewer

Because lignin limits the use of wood for fiber, chemical, and energy production, strategies for its downregulation are of considerable interest. We have produced transgenic aspen (Populus tremuloides Michx.) trees in which expression of a lignin biosynthetic pathway gene Pt4CL1 encoding 4-coumarate:coenzyme A ligase (4CL) has been downregulated by antisense inhibition. Trees with suppressed Pt4CL1 expression exhibited up to a 45% reduction of lignin, but this was compensated for by a 15% increase in cellulose. As a result, the total lignin–cellulose mass remained essentially unchanged. Leaf, root, and stem growth were substantially enhanced, and structural integrity was maintained both at the cellular and whole-plant levels in the transgenic lines. Our results indicate that lignin and cellulose deposition could be regulated in a compensatory fashion, which may contribute to metabolic flexibility and a growth advantage to sustain the long-term structural integrity of woody perennials.

Biotechnology on genetic control of lignin biosynthesis in trees -Repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees-

The characteristics of pollen tube growth are not constant, but display distinct patterns of growth within the different tissues of the pistil. In the stigma, the growth rate is slow and autotrophic, whereas in the style, it is rapid and heterotrophic. Very little is known about the interactions between these distinct maternal tissues and the traversing pollen tube and the role of this interaction on the observed metabolism. In this work we characterise pollen tube growth in the apple flower and look for differences in glycoprotein epitope localization between two different maternal tissues, the stigma and the style. While immunocytochemically-detected arabinogalactan proteins were present at high levels in the stigma, they were not detected in the transmitting tissue of the style, where extensins were abundant. Whereas extensins remained at high levels in unpollinated pistils, they were no longer present in the style following pollen tube passage. Similarily, while abundant in unpollinated styles, insoluble polysaccharides such as β-glucans, were depleted in pollinated pistils. The switch from autotropic to heterotrophic pollen tube growth correlates spatially with a change of glycoprotein epitopes between the stigma and the style. The depletion of extensins and polysaccharides following pollen tube passage in the style suggest a possible contribution to the acceleration of heterotrophic pollen tube growth, which would imply an active contribution of female tissues on prezygotic male–female crosstalk.

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Glycoprotein composition along the pistil of Malus x domestica and the modulation of pollen tube growth.

New insights into pectin methylesterase structure and function.

The apical wall of growing pollen tubes must be strong enough to withstand the internal turgor pressure, but plastic enough to allow the incorporation of new membrane and cell wall material to support polarized tip growth. These essential rheological properties appear to be controlled by pectins, which constitute the principal component of the apical cell wall. Pectins are secreted as methylesters and subsequently deesterified by the enzyme pectin methylesterase (PME) in a process that exposes acidic residues. These carboxyls can be cross-linked by calcium, which structurally rigidifies the cell wall. Here, we examine the role of PME in cell elongation and the regulation of its secretion and enzymatic activity. Application of an exogenous PME induces thickening of the apical cell wall and inhibits pollen tube growth. Screening a Nicotiana tabacum pollen cDNA library yielded a pollen-specific PME, NtPPME1, containing a pre-region and a pro-region. Expression studies with green fluorescent protein fusion proteins show that the pro-region participates in the correct targeting of the mature PME. Results from in vitro growth analysis and immunolocalization studies using antipectin antibodies (JIM5 and JIM7) provide support for the idea that the pro-region acts as an intracellular inhibitor of PME activity, thereby preventing premature deesterification of pectins. In addition to providing experimental data that help resolve the significance and function of the pro-region, our results give insight into the mechanism by which PME and its pro-region regulate the cell wall dynamics of growing pollen tubes.

Pectin methylesterase, a regulator of pollen tube growth

Pectic polysaccharides are an essential component of the primary plant cell wall. They are particularly prominent in pollen tubes, where they control the structure and yielding characteristics of the cell wall at the growing apex of these rapidly expanding cells. The properties of pectin meshworks,

Pectin Methylesterases and Pectin Dynamics in Pollen Tubes

We examined exocytosis during oscillatory growth in lily (Lilium formosanum and Lilium longiflorum) and tobacco (Nicotiana tabacum) pollen tubes using three markers: (1) changes in cell wall thickness by Nomarski differential interference contrast (DIC), (2) changes in apical cell wall fluorescence in cells stained with propidium iodide (PI), and (3) changes in apical wall fluorescence in cells expressing tobacco pectin methyl esterase fused to green fluorescent protein (PME-GFP). Using PI fluorescence, we quantified oscillatory changes in the amount of wall material from both lily and tobacco pollen tubes. Measurement of wall thickness by DIC was only possible with lily due to limitations of microscope resolution. PME-GFP, a direct marker for exocytosis, only provides information in tobacco because its expression in lily causes growth inhibition and cell death. We show that exocytosis in pollen tubes oscillates and leads the increase in growth rate; the mean phase difference between exocytosis and growth is –98° ± 3° in lily and –124° ± 4° in tobacco. Statistical analyses reveal that the anticipatory increase in wall material predicts, to a high degree, the rate and extent of the subsequent growth surge. Exocytosis emerges as a prime candidate for the initiation and regulation of oscillatory pollen tube growth.

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Exocytosis precedes and predicts the increase in growth in oscillating pollen tubes

Pollen-pistil interactions are critical early events regulating pollination and fertilization. Self-incompatibility (SI) is an important mechanism to prevent self-fertilization and inbreeding in higher plants. Although data implicate the involvement of reactive oxygen species (ROS) and nitric oxide (NO) in pollen-pistil interactions and the regulation of pollen tube growth, there has been a lack of studies investigating ROS and NO signaling in pollen tubes in response to defined, physiologically relevant stimuli. We have used live-cell imaging to visualize ROS and NO in growing Papaver rhoeas pollen tubes using chloromethyl-2′7′-dichlorodihydrofluorescein diacetate acetyl ester and 4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate and demonstrate that SI induces relatively rapid and transient increases in ROS and NO, with each showing a distinctive “signature” within incompatible pollen tubes. Investigating how these signals integrate with the SI responses, we show that Ca2+ increases are upstream of ROS and NO. As ROS/NO scavengers alleviated both the formation of SI-induced actin punctate foci and also the activation of a DEVDase/caspase-3-like activity, this demonstrates that ROS and NO act upstream of these key SI markers and suggests that they signal to these SI events. These data represent, to our knowledge, the first steps in understanding ROS/NO signaling triggered by this receptor-ligand interaction in pollen tubes.

/pdf/reactive-oxygen-species-and-nitric-oxide-mediate-actin-2liwgjo7zc.pdf

Reactive Oxygen Species and Nitric Oxide Mediate Actin Reorganization and Programmed Cell Death in the Self-Incompatibility Response of Papaver

The successful establishment of angiosperms on land is in part determined by their floral design. Because plants cannot move to find the ideal mate, they have developed a great variety of flowers to provide different mechanisms of pollen release, pollen transfer, and deposition of the pollen from

/pdf/pistil-factors-controlling-pollination-2vev29quu7.pdf

Maurice Bosch

Papers

Pectin methylesterase, a regulator of pollen tube growth

Pectin Methylesterases and Pectin Dynamics in Pollen Tubes

Exocytosis precedes and predicts the increase in growth in oscillating pollen tubes

Reactive Oxygen Species and Nitric Oxide Mediate Actin Reorganization and Programmed Cell Death in the Self-Incompatibility Response of Papaver

Pistil factors controlling pollination.