SummaryVirus-induced gene silencing (VIGS) is a powerful tool for functional analysis of genes in plants. A wide-host-range VIGS vector, which was developed based on the Cucumber mosaic virus (CMV), was tested for its ability to silence endogenous genes involved in flavonoid biosynthesis in soybean. Symptomless infection was established using a pseudorecombinant virus, which enabled detection of specific changes in metabolite content by VIGS. It has been demonstrated that the yellow seed coat phenotype of various

Abiotic stress influences the translation of mRNAs in plants. To gain a global view of the early translational response to abiotic stress, we investigated genome-wide changes in mRNA translation in Arabidopsis thaliana suspension cell cultures exposed to brief periods of two types of stress: elevated temperature (37 degrees C) and high salinity (200 mM NaCl). Microarray analyses revealed that polysome association of most transcripts, which were monitored by using polysomal- and non-polysomal-associated RNA pools, was variably depressed by both stresses within 10 min. We also inspected coordination of changes in translational profiles with transcriptional profiles, and found no simple correlations between the changes in these two processes under both stresses. In addition, we uncovered that the 10 min heat- and salt-inducible changes in polysome association of individual transcripts affected specific biological functions differently; some functional classes were recalcitrant to the overall depression, while others were hypersensitive to it. Heat and salt stresses imposed similar, but not identical, changes in polysome association of individual transcripts, and the functional categories with differential responses from all other genes (i.e. recalcitrant or hypersensitive functional categories) displayed some overlap between the two stresses, suggesting similar underlying mechanisms. Our results highlight the importance of dynamic changes in mRNA translation, which include selective translation and extensive repression of a subset of transcripts, in plant abiotic stress responses.

Glehnia littoralis F. Schmidt ssp. leiocarpa (Mathias) Hult. (Apiaceae), a species of ethnopharmacological interest in British Columbia, has antibacterial and antifungal properties. Antibacterial and antifungal compounds include two hitherto unreported polyine compounds, (9Z)1,9-heptadecadiene-4,6-diyne-3,8,11-triol and (10E)1,10-heptadecadiene-4,6-diyne-3,8,9-triol.

Plants produce jasmonic acid (JA) and its amino acid conjugate, jasmonoyl-L-isoleucine (JA-Ile) as major defense signals in response to wounding and herbivory. In rice (Oryza sativa), JA and JA-Ile rapidly increased after mechanical damage, and this increase was further amplified when the wounds were treated with oral secretions from generalist herbivore larvae, lawn armyworms (Spodoptera mauritia), revealing for the first time active perception mechanisms of herbivore-associated elicitor(s) in rice. In the rice genome, two OsJAR genes can conjugate JA and Ile and form JA-Ile in vitro; however, their function in herbivory-induced accumulation of JA-Ile has not been investigated. By functional characterization of TOS17 retrotransposon-tagged Osjar1 plants and their response to simulated herbivory, we show that OsJAR1 is essential for JA-Ile production in herbivore-attacked, field-grown plants. In addition, OsJAR1 was required for normal seed development in rice under field conditions. Our results suggest that OsJAR1 possesses at least two major functions in rice defense and development that cannot be complemented by the additional OsJAR2 gene function, although this gene previously showed overlapping enzyme activity in vitro.

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Translation of specific plant mRNAs is differentially regulated under certain abiotic stress conditions such as heat, oxygen deprivation and dehydration. The majority of transcripts exhibit varying degrees of translational repression, whereas a subset of transcripts escape such repression and remain actively translated. The underlying mechanisms that mediate this control, and in particular the identities of the regulatory RNA elements involved, remain poorly understood. Using a combined computational and experimental approach, we identified a novel cis-regulatory element in the 5 0 -untranslated region (5 0 -UTR) that affects differential translation in response to heat stress (HS) in Arabidopsis thaliana. First, we selected a set of genes with distinct translational responses to HS, based on our previously reported genome-wide data regarding changes in polysome loading induced by HS in A. thaliana cultured cells. We evaluated the 5 0 -UTRs of these messages for their ability to mediate expression, when fused to reporter mRNAs, in protoplasts under HS. The data from the reporter assay and the nucleotide sequences of the 5 0 -UTRs tested were used to define regulatory elements in the 5 0 -UTRs, with the help of a partial least square (PLS) regression model. The computational analysis using PLS and subsequent experimental characterization of a series of 5 0 -UTR mutants provided evidence that the 5 0 -proximal sequence of the 5 0 -UTR is a primary and position-dependent determinant of 5 0 -UTR-mediated differential translation in response to HS. Finally, we discuss the possible mechanism underlying HS regulation of differential mRNA translation.

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