No abstract

Vitamin E (VTE) content is a low heritability nutritional trait for which the genetic determinants are poorly understood. Here, we focus on a previously detected major tomato VTE quantitative trait loci (QTL; mQTL 9-2-6 ) and identify the causal gene as one encoding a 2-methyl-6-phytylquinol methyltransferase (namely VTE3 (1)) that catalyses one of the final steps in the biosynthesis of g-and a-tocopherols, which are the main forms of VTE. By reverse genetic approaches, expression analyses, siRNA profiling and DNA methylation assays, we demonstrate that mQTL 9-2-6 is an expression QTL associated with differential methylation of a SINE retrotransposon located in the promoter region of VTE3(1). Promoter DNA methylation can be spontaneously reverted leading to different epialleles affecting VTE3(1) expression and VTE content in fruits. These findings indicate therefore that naturally occurring epialleles are responsible for regulation of a nutritionally important metabolic QTL and provide direct evidence of a role for epigenetics in the determination of agronomic traits.

The genome of tobacco mosaic virus (TMV) encodes replicase protein(s), movement protein (MP), and capsid protein (CP). On infection, one or more viral proteins direct the assembly of virus replication complexes (VRCs), in association with host-derived membranes. The impact of CP-mediated resistance on the structures of the replication complexes was examined in nontransgenic and transgenic BY-2 cell lines that produce wild-type CP, mutant CP T42W , and Ds-Red, which was targeted to endoplasmic reticulum by using immunofluorescence and 3D microscopy. We developed a model of VRCs that shows a clear association of MP with and surrounding the endoplasmic reticulum. Replicase is located within the MP bodies, as well as isolated sites throughout the cell. CP surrounds the VRCs. CP enhances the production of MP and increases the size of the VRC; however, the mutant CP T42W reduces the amount of MP and interferes with the formation of VRCs. We propose a regulatory role of the CP in the establishment of the VRC. We suggest that the lack of formation of VRCs restricts the efficiency of virus replication and the formation of virus movement complexes, resulting in restriction of cell-cell spread of infection. This results in higher levels of plant CP-mediated protection provided by CP T42W . P ositive-strand RNA viruses share fundamental similarities in RNA replication despite differences in genome organization, virion morphology, and host range. On entering the cell, the messenger-sense genome is translated to yield a variety of proteins, some of which direct the assembly of virus replication complexes (VRCs) that are invariably associated with host membrane (1-4).The 6.3-kb (ϩ) sense RNA genome of tobacco mosaic virus (TMV) encodes two proteins essential for replication of the genome (replicase, 126͞183 kDa), a 30-kDa movement protein (MP) that is essential for cell-cell spread of infection, and a 17.5-kDa capsid protein (CP). Cytological studies of TMVinfected cells showed VRCs associated with cytoplasmatic inclusions bodies, called viroplasm [also called X-bodies (5)], that enlarge throughout infection. Electron microscopy revealed that these inclusion bodies contained ribosomes, tubules, and 126͞ 183-kDa replication proteins (6-9).Recent studies show that the 126-kDa protein associates with the endoplasmic reticulum (ER) in the absence of other viral proteins, and it was suggested that association may occur via either membrane-bound host proteins or a membrane insertion of an amphipathic helix detected in the protein (10). The MP behaves as an intrinsic membrane protein, promotes the formation of ER aggregates, and probably facilitates the establishment of TMV replication complexes that contain viral RNA, replicase, and MP (11-15).Transgenic plants that produce TMV CP interfere with disassembly of TMV and thereby confer resistance to TMV infection (16). Mutant CP that is changed at amino acid 42 [Thr-42 3 Trp (T42W)] interferes with virus disassembly. In addition, it reduces production of MP on infection, thereby reduci...