The chloroplastic DEVH‐box RNA helicase INCREASED SIZE EXCLUSION LIMIT 2 involved in plasmodesmata regulation is required for group II intron splicing

INCREASED SIZE EXCLUSION LIMIT 2 (ISE2) encodes a putative DEVH‐box RNA helicase originally identified through a genetic screening for Arabidopsis mutants altered in plasmodesmata (PD) aperture. Depletion of ISE2 also affects chloroplasts activity, decreases accumulation of photosynthetic pigments and alters expression of photosynthetic genes. In this work, we show the chloroplast localization of ISE2 and decipher its role in plastidic RNA processing and, consequently, PD function. Group II intron‐containing RNAs from chloroplasts exhibit defective splicing in ise2 mutants and ISE2‐silenced plants, compromising plastid viability. Furthermore, RNA immunoprecipitation suggests that ISE2 binds in vivo to several splicing‐regulated RNAs. Finally, we show that the chloroplast clpr2 mutant (defective in a subunit of a plastidic Clp protease) also exhibits abnormal PD function during embryogenesis, supporting the idea that chloroplast RNA processing is required to regulate cell–cell communication in plants.     

The DEAD-box RNA helicase ZmRH48 is required for the splicing of multiple mitochondrial introns,mitochondrial complex biosynthesis,and seed development in maize

RNA helicases participate in nearly all aspects of RNA metabolism by rearranging RNAs or RNA–protein complexes in an adenosine triphosphatedependent manner. Due to the large RNA helicase families in plants, the precise roles of many RNA helicases in plant physiology and development remain to be clarified. Here, we show that mutations in maize(Zea mays) DEAD-box RNA helicase48(Zm RH48) impair the splicing of mitochondrial introns, mitochondrial complex biosynthesis,and seed development. Loss of Z...     

Interplay of cis- and trans-regulatory mechanisms in the spliceosomal RNA helicase Brr2

RNA helicase Brr2 is implicated in multiple phases of pre-mRNA splicing and thus requires tight regulation. Brr2 can be auto-inhibited via a large N-terminal region folding back onto its helicase core and auto-activated by a catalytically inactive C-terminal helicase cassette. Furthermore, it can be regulated in trans by the Jab1 domain of the Prp8 protein, which can inhibit Brr2 by intermittently inserting a C-terminal tail in the enzyme's RNA-binding tunnel or activate the helicase after removal of this tail. Presently it is unclear, whether these regulatory mechanisms functionally interact and to which extent they are evolutionarily conserved. Here, we report crystal structures of Saccharomyces cerevisiae and Chaetomium thermophilum Brr2-Jab1 complexes, demonstrating that Jab1-based inhibition of Brr2 presumably takes effect in all eukaryotes but is implemented via organism-specific molecular contacts. Moreover, the structures show that Brr2 auto-inhibition can act in concert with Jab1-mediated inhibition, and suggest that the N-terminal region influences how the Jab1 C-terminal tail interacts at the RNA-binding tunnel. Systematic RNA binding and unwinding studies revealed that the N-terminal region and the Jab1 C-terminal tail specifically interfere with accommodation of double-stranded and single-stranded regions of an RNA substrate, respectively, mutually reinforcing each other. Additionally, such analyses show that regulation based on the N-terminal region requires the presence of the inactive C-terminal helicase cassette. Together, our results outline an intricate system of regulatory mechanisms, which control Brr2 activities during snRNP assembly and splicing.