Expression Elements Derived From Plant Sequences Provide Effective Gene Expression Regulation and New Opportunities for Plant Biotechnology Traits.

Plant biotechnology traits provide a means to increase crop yields, manage weeds and pests, and sustainably contribute to addressing the needs of a growing population. One of the key challenges in developing new traits for plant biotechnology is the availability of expression elements for efficacious and predictable transgene regulation. Recent advances in genomics, transcriptomics, and computational tools have enabled the generation of new expression elements in a variety of model organisms.

Transcriptional silencing induced by Arabidopsis T-DNA mutants is associated with 35S promoter siRNAs and requires genes involved in siRNA-mediated chromatin silencing.

The utility of many T-DNA insertion mutant lines of Arabidopsis is compromised by their propensity to trigger transcriptional silencing of transgenes expressed from the CaMV 35S promoter. To try to circumvent this problem, we characterized the genetic requirements for maintenance of 35S promoter homology-dependent transcriptional gene silencing induced by the dcl3-1 (SALK_005512) T-DNA insertion mutant line. Surprisingly, even though DCL3 and RDR2 are known components of the siRNA-dependent transcriptional gene silencing pathway, transcriptional gene silencing of a 35S promoter-driven GUS hairpin transgene did occur in plants homozygous for the dcl3-1 T-DNA insertion and was unaffected by loss of function of RDR2.

An RNA polymerase II- and AGO4-associated protein acts in RNA-directed DNA methylation.

DNA methylation is an important epigenetic mark in many eukaryotes. In plants, 24-nucleotide small interfering RNAs (siRNAs) bound to the effector protein, Argonaute 4 (AGO4), can direct de novo DNA methylation by the methyltransferase DRM2 (refs 2, 4-6). Here we report a new regulator of RNA-directed DNA methylation (RdDM) in Arabidopsis: RDM1.

Two plant viral suppressors of silencing require the ethylene-inducible host transcription factor RAV2 to block RNA silencing.

RNA silencing is a highly conserved pathway in the network of interconnected defense responses that are activated during viral infection. As a counter-defense, many plant viruses encode proteins that block silencing, often also interfering with endogenous small RNA pathways. However, the mechanism of action of viral suppressors is not well understood and the role of host factors in the process is just beginning to emerge.

The potyvirus recessive resistance gene, sbm1, identifies a novel role for translation initiation factor eIF4E in cell-to-cell trafficking.

From the characterization of the recessive resistance gene, sbm1, in pea we have identified the eukaryotic translation initiation factor, eIF4E, as a susceptibility factor required for infection with the Potyvirus, Pea seed-borne mosaic virus. A functional analysis of the mode of action of the product of the dominant allele revealed a novel function for eIF4E in its support for virus movement from cell-to-cell, in addition to its probable support for viral RNA translation, and hence replication. Different resistance specificities in two independent pea lines were explained by different mutations in eIF4E.