The resistance to a set of strains of Cucumber mosaic virus (CMV) in the melon accession PI 161375, cultivar 'Songwhan Charmi', is dependent on one recessive gene, cmv1, which confers total resistance, whereas a second set of strains is able to overcome it. We tested 11 strains of CMV subgroups I and II in the melon line SC12-1-99, which carries the gene cmv1, and showed that this gene confers resistance to strains of subgroup II only and that restriction is not related to either viral replication or cell-to-cell movement. This is the first time that a resistant trait has been correlated with CMV subgroups. Using infectious clones of the CMV strains LS (subgroup II) and FNY (subgroup I), we generated rearrangements and viral chimaeras between both strains and established that the determinant of virulence against the gene cmv1 resides in the first 209 amino acids of the movement protein, as this region from FNY is sufficient to confer virulence to the LS clone in the line SC12-1-99. A comparison of the sequences of the strains of both subgroups in this region shows that there are five main positions shared by all strains of subgroup II, which are different from those of subgroup I. Site-directed mutagenesis of the CMV-LS clone to substitute these residues for those of CMV-FNY revealed that a combination of four of these changes [the group 64-68 (SNNLL to HGRIA), and the point mutations R81C, G171T and A195I] was required for a complete gain of function of the LS MP in the resistant melon plant.

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SUMMARYCucumber mosaic virus (CMV) has the broadest host range among plant viruses, causing enormous losses in agriculture. In melon, strains of subgroup II are unable to establish a systemic infection in the near-isogenic line SC12-1-99, which carries the recessive resistance gene cmv1 from the accession PI 161375, cultivar 'Songwhan Charmi'. Strains of subgroup I overcome cmv1 resistance in a manner dependent on the movement protein. We characterized the resistance conferred by cmv1 and established that CMV-LS (subgroup II) can move from cell to cell up to the veins in the inoculated leaf, but cannot enter the phloem. Immunogold labelling at transmission electron microscopy level showed that CMV-LS remains restricted to the bundle sheath (BS) cells in the resistant line, and does not invade vascular parenchyma or intermediary cells, whereas, in the susceptible line 'Piel de Sapo' (PS), the virus invades all vein cell types. These observations indicate that the resistant allele of cmv1 restricts systemic infection in a virus strain-and cell type-specific manner by acting as an important gatekeeper for virus progression from BS cells to phloem cells. Graft inoculation experiments showed that CMV-LS cannot move from the infected PS stock into the resistant cmv1 scion, thus suggesting an additional role for cmv1 related to CMV transport within or exit from the phloem. The characterization of this new form of recessive resistance, based on a restriction of virus systemic movement, opens up the possibility to design alternative approaches for breeding strategies in melon.

A laboratory experiment was conducted to identify key hydrocarbon degraders from a marine oil spill sample (Prestige fuel oil), to ascertain their role in the degradation of different hydrocarbons, and to assess their biodegradation potential for this complex heavy oil. After a 17-month enrichment in weathered fuel, the bacterial community, initially consisting mainly of Methylophaga species, underwent a major selective pressure in favor of obligate hydrocarbonoclastic microorganisms, such as Alcanivorax and Marinobacter spp. and other hydrocarbon-degrading taxa (Thalassospira and Alcaligenes), and showed strong biodegradation potential. This ranged from >99% for all low- and medium-molecular-weight alkanes (C(15)-C(27)) and polycyclic aromatic hydrocarbons (C(0)- to C(2)- naphthalene, anthracene, phenanthrene, dibenzothiophene, and carbazole), to 75-98% for higher molecular-weight alkanes (C(28)-C(40)) and to 55-80% for the C(3) derivatives of tricyclic and tetracyclic polycyclic aromatic hydrocarbons (PAHs) (e.g., C(3)-chrysenes), in 60 days. The numbers of total heterotrophs and of n-alkane-, aliphatic-, and PAH degraders, as well as the structures of these populations, were monitored throughout the biodegradation process. The salinity of the counting medium affects the counts of PAH degraders, while the carbon source (n-hexadecane vs. a mixture of aliphatic hydrocarbons) is a key factor when counting aliphatic degraders. These limitations notwithstanding, some bacterial genera associated with hydrocarbon degradation (mainly belonging to α- and γ-Proteobacteria, including the hydrocarbonoclastic Alcanivorax and Marinobacter) were identified. We conclude that Thalassospira and Roseobacter contribute to the degradation of aliphatic hydrocarbons, whereas Mesorhizobium and Muricauda participate in the degradation of PAHs.

Peroxiredoxins (Prx) catalyse the reduction of hydrogen peroxide (H2O2) and, in association with catalases and other peroxidases, may participate in signal transduction by regulating intercellular H2O2 concentration that in turn can control gene transcription and cell signaling. Using virus-induced-gene-silencing (VIGS), 2-Cys Peroxiredoxin (2CysPrx) family and type-II Peroxiredoxin B (PrxIIB) gene were silenced in Nicotiana benthamiana, to study the impact that the loss of function of each Prx would have in the antioxidant system under control (22 °C) and severe heat stress conditions (48 °C). The results showed that both Prxs, although in different organelles, influence the regeneration of ascorbate to a significant extent, but with different purposes. 2CysPrx affects abscisic acid (ABA) biosynthesis through ascorbate, while PrxIIB does it probably through the xanthophyll cycle. Moreover, 2CysPrx is key in H2O2 scavenging and in consequence in the regulation of ABA signaling downstream of reactive oxygen species and PrxIIB provides an important assistance for H2O2 peroxisome scavenges.