Sly-miR166 and Sly-miR319 are components of the cold stress response in Solanum lycopersicum

MicroRNAs (miRNAs) are a class of small endogenous non-coding RNAs that modulate gene expression in both plants and animals and are involved in several biological processes, ranging from organ differentiation to biotic and abiotic stress responses. We identified two cold stress response microRNAs that showed differential expression in Solanum lycopersicum plants subjected to cold stress. We observed that Sly-miR166 and Sly-miR319 were up-regulated by cold treatments. The up-regulation of Sly-miR166 and Sly-miR319 in cold stress-treated S. lycopersicum seedlings and the down-regulation of their respective targets, HD-Zip III and GAMyb-like that validate by 5′-RACE technique, suggests that these miRNAs play a critical role in regulating S. lycopersicum responses to cold stress.     

Influence of gag and RRE Sequences on HIV-1 RNA Packaging Signal Structure and Function

The packaging signal (Ψ) and Rev-responsive element (RRE) enable unspliced HIV-1 RNAs' export from the nucleus and packaging into virions. For some retroviruses, engrafting Ψ onto a heterologous RNA is sufficient to direct encapsidation. In contrast, HIV-1 RNA packaging requires 5′ leader Ψ elements plus poorly defined additional features. We previously defined minimal 5′ leader sequences competitive with intact Ψ for HIV-1 packaging, and here examined the potential roles of additional downstream elements. The findings confirmed that together, HIV-1 5′ leader Ψ sequences plus a nuclear export element are sufficient to specify packaging. However, RNAs trafficked using a heterologous export element did not compete well with RNAs using HIV-1's RRE. Furthermore, some RNA additions to well-packaged minimal vectors rendered them packaging-defective. These defects were rescued by extending gag sequences in their native context. To understand these packaging defects' causes, in vitro dimerization properties of RNAs containing minimal packaging elements were compared to RNAs with sequence extensions that were or were not compatible with packaging. In vitro dimerization was found to correlate with packaging phenotypes, suggesting that HIV-1 evolved to prevent 5′ leader residues' base pairing with downstream residues and misfolding of the packaging signal. Our findings explain why gag sequences have been implicated in packaging and show that RRE's packaging contributions appear more specific than nuclear export alone. Paired with recent work showing that sequences upstream of Ψ can dictate RNA folds, the current work explains how genetic context of minimal packaging elements contributes to HIV-1 RNA fate determination.