Plants use both cell surface-resident pattern recognition receptors (PRRs) and intracellular nucleotide binding leucine-rich repeat (NLR) receptors to detect various pathogens. Plant PRRs typically recognize conserved pathogen-associated molecular patterns (PAMPs) to provide broad-spectrum resistance. By contrast, plant NLRs generally detect pathogen strain-specific effectors and confer race-specific resistance. Here, we demonstrate that the tomato () NLR Sw-5b confers broad-spectrum resistance against American-type tospoviruses by recognizing a conserved 21-amino acid peptide region within viral movement protein NSm (NSm). Sw-5b NB-ARC-LRR domains directly associate with NSm in vitro and in planta. Domain swap, site-directed mutagenesis and structure modeling analyses identified four polymorphic sites in the Sw-5b LRR domain that are critical for the recognition of NSm Furthermore, recognition of NSm by Sw-5b likely disturbs the residues adjacent to R927 in the LRR domain to weaken the intramolecular interaction between LRR and NB-ARC domains, thus translating recognition of NSm into activation of Sw-5b. Natural variation analysis of Sw-5b homologs from wild tomato species of South America revealed that the four polymorphic sites in the Sw-5b LRR domain were positively selected during evolution and are all necessary to confer resistance to tospovirus. The results described here provide a new example of a plant NLR mediating broad-spectrum resistance through recognition of a small conserved PAMP-like region within the pathogen effector.

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The dysmyelinating mutant jimpy ( jp) arises from a point mutation in the mouse gene encoding proteolipid protein and is characterized by severe dysmyelination attributable to oligodendrocyte death. This mutant was used to investigate the regulation of oligodendrocyte progenitor proliferation in the postnatal spinal cord. At postnatal day 18, jp spinal cord contained a three-to eightfold greater number of proliferating oligodendrocyte progenitor cells than did wild-type (wt) spinal cord. Increased proliferation in jp spinal cord was accompanied by a twofold increase in the number of progenitor cells. Semiquantitative reverse transcriptase-PCR revealed no change in the level of mRNA encoding the platelet-derived growth factor A, transforming growth factor-␤, or insulin-like growth factor-I, all of which have been implicated as regulators of proliferation and differentiation of oligodendrocyte progenitor cells. There was, however, a 17-fold increase in the level of mRNA encoding the chemokine GRO-1 and a 5-to 6-fold increase in GRO-1 protein in the jp spinal cord. Double immunofluorescence labeling revealed elevated levels of GRO-1 in reactive astrocytes in jp spinal cord white matter. In vitro studies indicated that extracts from jp spinal cord stimulated oligodendrocyte progenitor proliferation. Furthermore, removal of GRO-1 from jp extracts by immunoprecipitation reduced the proliferation of progenitor cells to a level similar to that achieved by wt extracts. These findings suggest a novel mechanism by which proliferation of oligodendrocyte progenitor cells is regulated in the postnatal spinal cord in response to insult.

Glial cells that express the NG2 proteoglycan (NG2(+) cells) are considered to be oligodendrocyte progenitors (OPCs) in the central nervous system (CNS), based on their ability to give rise to mature oligodendrocytes in vitro. To understand how dysmyelinated conditions influence OPC proliferation and differentiation, we studied proliferation and differentiation of NG2(+) OPCs in vivo in the shiverer mutant (shi), which do not form compact myelin due to a deletion in the myelin basic protein gene. Acute bromodeoxyuridine (BrdU) labeling studies revealed a 4- to 6-fold increase in NG2(+) cell proliferation in shi spinal cord between postnatal day18 (P18) and P60, and most BrdU(+) cells were NG2(+) after P18. The increased proliferation was accompanied by a 2-fold increase in the number of OPCs and oligodendrocytes. Survival studies following a single injection of BrdU at P18 revealed a decline in the number of BrdU(+)/NG2(+) cells with a concomitant increase in the number of BrdU(+) oligodendrocytes over time, suggesting that the proliferated NG2(+) cells had differentiated into oligodendrocytes. BrdU(+) oligodendrocytes were generated over a longer period of time in shi spinal cord and persisted longer in shi than in wild type spinal cord. These findings suggest that new oligodendrocytes continue to be generated in the dysmyelinated shi spinal cord by enhanced proliferation and differentiation of NG2(+) oligodendrocyte progenitor cells.

Exposure of cells to protein tyrosine phosphatase (PTP) inhibitors causes an increase in the phosphotyrosine content of many cellular proteins. However, the level at which the primary signaling event is affected is still unclear. We show that Jaks are activated by tyrosine phosphorylation in cells that are brief ly exposed to the PTP inhibitor pervanadate (PV), resulting in tyrosine phosphorylation and functional activation of Stat6 (in addition to other Stats). Mutant cell lines that lack Jak1 activity fail to support PV-mediated Cytokines transmit their signals through transmembrane receptors that are physically associated with members of the Jak family of protein tyrosine kinases (PTK) (1-8). Aggregation of receptors, resulting in the association of Jaks in a receptor complex and a conformational change in the kinase domain, is an early step in cytokine receptor activation (2-11). Transphosphorylation of the conserved tyrosine residues in the kinase activation segments promotes kinase activity (11). The activated Jaks then phosphorylate the receptor-associated and downstream signaling molecules, including Stat proteins recruited to the receptor complex (1)(2)(3)(4)(5)(6)(7)(8)(12)(13)(14)(15).Protein tyrosine phosphatases (PTP) are associated with many cytokine receptors and are implicated in the downregulation of ligand-induced signaling through dephosphorylation of the activated Jaks and the receptors (15)(16)(17)(18)(19)(20). Dephosphorylation of activated Stat proteins is catalyzed by different PTP activities in the nucleus (21-23). We and others have found that cytokine receptor-associated PTP activities not only down-regulate cytokine-induced signals but also suppress the constitutive activities of Jak proteins (21,(24)(25)(26).

Background and Aims Root diameter, especially apical diameter, plays an important role in root development and function. The variation in diameter between roots, and along roots, affects root structure and thus the root system's overall foraging performance. However, the effect of diameter variation on root elongation, branching and topological connections has not been examined systematically in a population of high-order roots, nor along the roots, especially for mature plants grown in the field.Methods A method combining both excavation and analysis was applied to extract and quantify root architectural traits of adult, field-grown maize plants. The relationships between root diameter and other root architectural characteristics are analysed for two maize cultivars.Key Results The basal diameter of the lateral roots (orders 1-3) was highly variable. Basal diameter was partly determined by the diameter of the bearing segment. Basal diameter defined a potential root length, but the lengths of most roots fell far short of this. This was explained partly by differences in the pattern of diameter change along roots. Diameter tended to decrease along most roots, with the steepness of the gradient of decrease depending on basal diameter. The longest roots were those that maintained (or sometimes increased) their diameters during elongation. The branching density (cm -1 ) of laterals was also determined by the diameter of the bearing segment. However, the location of this bearing segment along the mother root was also involved -intermediate positions were associated with higher densities of laterals.Conclusions The method used here allows us to obtain very detailed records of the geometry and topology of a complex root system. Basal diameter and the pattern of diameter change along a root were associated with its final length. These relationships are especially useful in simulations of root elongation and branching in source-sink models.

Endoplasmic reticulum (ER) membrane junctions are formed by the dynamin-like GTPase atlastin (ATL). Deletion of ATL results in long unbranched ER tubules in cells, and mutation of human ATL1 is linked to hereditary spastic paraplegia. Here, we demonstrate that COPII formation is drastically decreased in the periphery of ATL-deleted cells. ER export of cargo proteins becomes defective; ER exit site initiation is not affected, but many of the sites fail to recruit COPII subunits. The efficiency of cargo packaging into COPII vesicles is significantly reduced in cells lacking ATLs, or when the ER is transiently fragmented. Cargo is less mobile in the ER in the absence of ATL, but the cargo mobility and COPII formation can be restored by ATL R77A, which is capable of tethering, but not fusing, ER tubules. These findings suggest that the generation of ER junctions by ATL plays a critical role in maintaining the necessary mobility of ER contents to allow efficient packaging of cargo proteins into COPII vesicles.

As a signaling molecule, jasmonate plays a crucial role in orchestrating plant defense responses to a variety of biotic and abiotic stresses. Allene oxide cyclase (AOC: EC5.3.99.6) catalyzes the most important step in the jasmonate biosynthesis pathway. Six AOC genes were isolated from soybean, randomly distributed on chromosomes 1, 2, 8, 13, 18 and 19. The six AOC proteins were clustered into three groups with similarity values ranging from 55 to 95%. Real-time PCR revealed that the AOC genes have specific and complex expression patterns in multiple organs and under several stresses. Overexpression of GmAOC1 and GmAOC5 gene in transgenic tobacco, respectively enhanced tolerance to salinity and oxidative stresses. Such a large diversity within the AOC gene family might be an adaptive mechanism that developed during soybean genome evolution.