Mohammed Bendahmane

BIGPETALp, a bHLH transcription factor is involved in the control of Arabidopsis petal size

In Arabidopsis, APETALA1, PISTILLATA, APETALA3 and SEPALLATA interact to form multimeric protein complexes required to specify petal identity. However, the downstream events that lead to petal specific shape and size remain largely unknown. Organ final size can be influenced by cell number or cell expansion or both. To date, no gene that specifically limits petal size by controlling postmitotic cell expansion has been identified. Here we have identified a novel petal‐expressed, basic helix‐loop‐helix encoding gene (BIGPETAL, BPE) that is involved in the control of petal size. BPE is expressed via two mRNAs derived from an alternative splicing event. The BPEub transcript is expressed ubiquitously, whereas the BPEp transcript is preferentially expressed in petals. We demonstrate that BPEp is positively regulated downstream of APETALA3, PISTILLATA, APETALA1 and PISTILLATA3 and is negatively regulated downstream of AGAMOUS. Plants that lack the petal‐expressed variant BPEp have larger petals as a result of increased cell size, showing that BPEp interferes with postmitotic cell expansion. BPEp is therefore a part of the network that links the patterning genes to final morphogenesis.

Engineering resistance against tomato yellow leaf curl virus (TYLCV) using antisense RNA.

One of the most severe diseases of cultivated tomato worldwide is caused by tomato yellow leaf curl virus (TYLCV), a geminivirus transmitted by the whitefly Bemisia tabaci. Here we describe the application of antisense RNAs to interfere with the disease caused by TYLCV. The target of the antisense RNA is the rare messenger RNA of the Rep protein, encoded by the C1 gene. Transgenic Nicotiana benthamiana plants expressing C1 antisense RNA were obtained and shown to resist infection by TYLCV. Some of the resistant lines are symptomless, and the replication of challenge TYLCV almost completely suppressed. The transgenes mediating resistance were shown to be effective through at least two generations of progeny.

Translationally controlled tumor protein is a conserved mitotic growth integrator in animals and plants.

The growth of an organism and its size determination require the tight regulation of cell proliferation and cell growth. However, the mechanisms and regulatory networks that control and integrate these processes remain poorly understood. Here, we address the biological role of Arabidopsis translationally controlled tumor protein (AtTCTP) and test its shared functions in animals and plants. The data support a role of plant AtTCTP as a positive regulator of mitotic growth by specifically controlling the duration of the cell cycle. We show that, in contrast to animal TCTP, plant AtTCTP is not implicated in regulating postmitotic growth. Consistent with this finding, plant AtTCTP can fully rescue cell proliferation defects in Drosophila loss of function for dTCTP. Furthermore, Drosophila dTCTP is able to fully rescue cell proliferation defects in Arabidopsis tctp knockouts. Our data provide evidence that TCTP function in regulating cell division is part of a conserved growth regulatory pathway shared between plants and animals. The study also suggests that, although the cell division machinery is shared in all multicellular organisms to control growth, cell expansion can be uncoupled from cell division in plants but not in animals.

Analysis of gene expression in rose petals using expressed sequence tags

Single‐pass sequences were obtained from the 5′‐ends of a total of 1794 rose petal cDNA clones. Cluster analysis identified 242 groups of sequences and 635 singletons indicating that the database represents a total of 877 genes. Putative functions could be assigned to 1151 of the transcripts. Expression analysis indicated that transcripts of several of the genes identified accumulated specifically in petals and stamens. The cDNA library and expressed sequence tag database described here represent a valuable resource for future research aimed at improving economically important rose characteristics such as flower form, longevity and scent.

Immunization with a chimeric tobacco mosaic virus containing an epitope of outer membrane protein F of Pseudomonas aeruginosa provides protection against challenge with P. aeruginosa.

A chimeric tobacco mosaic virus (TMV) was constructed by inserting sequences representing peptide 9-14mer (TDAYNQKLSERRAN) of outer membrane (OM) protein F of Pseudomonas aeruginosa between amino acids Ser154 and Gly155 of the TMV coat protein (CP). This is the first example of TMV being used to construct a chimera containing a bacterial epitope. Mice immunized with TMV-9-14 produced anti-peptide-9-14mer-specific antibodies that reacted in whole-cell ELISA with all seven Fisher-Devlin (FD) immunotype strains of P. aeruginosa, reacted specifically by Western blotting with OM protein F extracted from all seven FD immunotypes, and were opsonic in opsonophagocytic assays. The chimeric TMV-9-14 vaccine afforded immunoprotection against challenge with wild-type P. aeruginosa in a mouse model of chronic pulmonary infection. TMV-9-14 is an excellent candidate for further development as a vaccine for possible use in humans to protect against P. aeruginosa infections.

Biosynthesis of the major scent components 3,5-dimethoxytoluene and 1,3,5-trimethoxybenzene by novel rose O-methyltransferases

In Chinese rose species and in many modern varieties, two methylated phenolic derivatives, 3,5‐dimethoxytoluene and 1,3,5‐trimethoxybenzene, are major scent components. We show that cell‐free extracts of rose petals catalyse the synthesis of 3,5‐dimethoxytoluene and 1,3,5‐trimethoxybenzene by methylation of precursor molecules. An expressed sequence tag approach was used to identify four highly similar O‐methyltransferase sequences expressed specifically in petals and anthers. Thin layer chromatography analysis showed that the activities of these enzymes with different substrates and the proportions of reaction products produced closely mimicked those observed using cell‐free petal extracts, indicating that orcinol O‐methyltransferases are responsible for the biosynthesis of 3,5‐dimethoxytoluene and 1,3,5‐trimethoxybenzene from un‐methylated precursors in this organ.

Development of Tobacco Mosaic Virus Infection Sites in Nicotiana benthamiana

To monitor infection of Nicotiana benthamiana by tobacco mosaic virus (TMV), leaves were inoculated with viral constructs expressing the green fluorescent protein (GFP) from jellyfish (Aequorea victoria) fused to the movement protein (MP) of TMV (MP:GFP) or as a free GFP in place of the coat protein (CP). Infection sites produced by TMV expressing the MP:GFP appeared as fluorescent rings larger in diameter and less fluorescent than fluorescent disks induced by constructs encoding free GFP. These results suggest that protein expression driven by the MP subgenomic promoter (sgp) initiates and ends earlier and is at lower level than that observed for proteins driven by the CP sgp. Similarly, analyses of cross sections through the infection sites revealed that in different cell types the accumulation of MP:GFP was regulated differently than the accumulation of free GFP. Immunocytochemistry and electron microscopy showed that near the leading edge of the fluorescent ring the MP:GFP and the viral 126 kDa and 18...

Scent evolution in Chinese roses

The phenolic methyl ether 3,5-dimethoxytoluene (DMT) is a major scent compound of many modern rose varieties, and its fragrance participates in the characteristic “tea scent” that gave their name to Tea and Hybrid Tea roses. Among wild roses, phenolic methyl ether (PME) biosynthesis is restricted to Chinese rose species, but the progenitors of modern roses included both European and Chinese species (e.g., Rosa chinensis cv Old Blush), so this trait was transmitted to their hybrid progeny. The last steps of the biosynthetic pathways leading to DMT involve two methylation reactions catalyzed by the highly similar orcinol O-methyltransferases (OOMT) 1 and 2. OOMT1 and OOMT2 enzymes exhibit different substrate specificities that are consistent with their operating sequentially in DMT biosynthesis. Here, we show that these different substrate specificities are mostly due to a single amino acid polymorphism in the phenolic substrate binding site of OOMTs. An analysis of the OOMT gene family in 18 species representing the diversity of the genus Rosa indicated that only Chinese roses possess both the OOMT2 and the OOMT1 genes. In addition, we provide evidence that the Chinese-rose-specific OOMT1 genes most probably evolved from an OOMT2-like gene that has homologues in the genomes of all extant roses. We propose that the emergence of the OOMT1 gene may have been a critical step in the evolution of scent production in Chinese roses.

Characterization of mutant tobacco mosaic virus coat protein that interferes with virus cell-to-cell movement

Expression of tobacco mosaic virus (TMV) coat protein (CP) in plants confers resistance to infection by TMV and related tobamoviruses. Certain mutants of the CP (CPT42W) provide much greater levels of resistance than wild-type (wt) CP. In the present work, infection induced by RNA transcripts of TMV clones that contain wt CP or mutant CPT42W fused to the green fluorescent protein (GFP) (TMV-CP:GFP, TMV-CPT42W:GFP) and clones harboring TMV movement protein (MP):GFP were followed in nontransgenic and transgenic tobacco BY-2 protoplasts and Nicotiana tabaccum Xanthi-nn plants that express wt CP or CPT42W. On nontransgenic and wt CP transgenic plants, TMV-CP:GFP produced expanding, highly fluorescent disk-shaped areas. On plants expressing CPT42W, infection by TMV-CP:GFP or TMV-MP:GFP-CP produced infection sites of smaller size that were characterized by low fluorescence, reflecting reduced levels of virus spread and reduced accumulation of both CP:GFP and MP:GFP. TMV-CPT42W:GFP failed to produce visible infection sites on nontransgenic plants, yet produced normal infection sites on MP-transgenic plants that produce MP. TMV infection of transgenic BY-CPT42W protoplasts resulted in very low levels of MP accumulation, whereas on BY-CP protoplasts (containing wt CP), infection produced higher levels of MP than in nontransgenic BY-2 cells. The results suggest that wt CP has a positive effect on the production of MP, whereas the CPT42W has a negative effect on MP accumulation and/or function. This effect results in very high levels of resistance to TMV infection in plants containing CPT42W. This report shows that the CP of a plant virus regulates production of the MP, and that a mutant CP interferes with MP accumulation and cell-to-cell movement of infection.

Tinkering with the C-function: a molecular frame for the selection of double flowers in cultivated roses.

Background Roses have been cultivated for centuries and a number of varieties have been selected based on flower traits such as petal form, color, and number. Wild-type roses have five petals (simple flowers), whereas high numbers of petals (double flowers) are typical attributes of most of the cultivated roses. Here, we investigated the molecular mechanisms that could have been selected to control petal number in roses. Methodology/Principal Findings We have analyzed the expression of several candidate genes known to be involved in floral organ identity determination in roses from similar genetic backgrounds but exhibiting contrasting petal numbers per flower. We show that the rose ortholog of AGAMOUS (RhAG) is differentially expressed in double flowers as compared to simple flowers. In situ hybridization experiments confirm the differential expression of RhAG and demonstrate that in the double-flower roses, the expression domain of RhAG is restricted toward the center of the flower. Conversely, in simple-flower roses, RhAG expression domain is wider. We further show that the border of RhAG expression domain is labile, which allows the selection of rose flowers with increased petal number. Double-flower roses were selected independently in the two major regions for domestication, China and the peri-Mediterranean areas. Comparison of RhAG expression in the wild-type ancestors of cultivated roses and their descendants both in the European and Chinese lineages corroborates the correlation between the degree of restriction of RhAG expression domain and the number of petals. Our data suggests that a restriction of RhAG expression domain is the basis for selection of double flowers in both the Chinese and peri-Mediterranean centers of domestication. Conclusions/Significance We demonstrate that a shift in RhAG expression domain boundary occurred in rose hybrids, causing double-flower phenotype. This molecular event was selected independently during rose domestication in Europe/Middle East and in China.