SINE RNA Induces Severe Developmental Defects in Arabidopsis thaliana and Interacts with HYL1 (DRB1), a Key Member of the DCL1 Complex

The proper temporal and spatial expression of genes during plant development is governed, in part, by the regulatory activities of various types of small RNAs produced by the different RNAi pathways. Here we report that transgenic Arabidopsis plants constitutively expressing the rapeseed SB1 SINE retroposon exhibit developmental defects resembling those observed in some RNAi mutants. We show that SB1 RNA interacts with HYL1 (DRB1), a double-stranded RNA-binding protein (dsRBP) that associates with the Dicer homologue DCL1 to produce microRNAs. RNase V1 protection assays mapped the binding site of HYL1 to a SB1 region that mimics the hairpin structure of microRNA precursors. We also show that HYL1, upon binding to RNA substrates, induces conformational changes that force single-stranded RNA regions to adopt a structured helix-like conformation. Xenopus laevis ADAR1, but not Arabidopsis DRB4, binds SB1 RNA in the same region as HYL1, suggesting that SINE RNAs bind only a subset of dsRBPs. Consistently, DCL4-DRB4-dependent miRNA accumulation was unchanged in SB1 transgenic Arabidopsis, whereas DCL1-HYL1-dependent miRNA and DCL1-HYL1-DCL4-DRB4-dependent tasiRNA accumulation was decreased. We propose that SINE RNA can modulate the activity of the RNAi pathways in plants and possibly in other eukaryotes

Egg production across a 40-week period in the phasmid Sipyloidea sp. (Diapheromeridae) from a tropical rain forest, north Queensland, Australia

In this study we report the results from the first long-term (40 weeks) study of stick-insect fecundity and distribution under natural conditions of which we are aware. We used the number of eggs falling into 72 × 0.5 m^2 traps to ask: 'Was egg production in Sipyloidea sp. uniform across the sample period'? and 'Was there evidence of host plant species preference or avoidance'? We collected a total of 213 Sipyloidea sp. eggs. The number of eggs caught per week was not uniform and an exponential decay model was the best-fit relationship between egg production and time, indicative of a steep decline from high to low (but continuous) egg production across the study period. Continuous egg production differs from other insect species in tropical areas that often show distinct seasonal differences between wet and dry seasons, timed to leaf production in host plants. The distribution of eggs within traps was aggregated, and more traps than expected from Poisson probabilities received no eggs, or six or more eggs. The concentration of eggs within particular traps was not related to the identity of canopy plant species, however. We suggest that continuous egg production in Sipyloidea sp. may be related to the wider range of plant species available as food resources for the polyphagous Sipyloidea, compared with other tropical insect species