Abstract
The exosome complex plays a central and essential role in RNA metabolism. However, current research on functions of exosome subunit in plants is limited. Here, we used an egg cell-specific promoter-controlled CRISPR/Cas9 system to knock out RRP42 which encodes a core subunit of the Arabidopsis exosome and presented evidence that RRP42 is essential for the development of female gametophytes. Next, we designed three different amiRNAs targeting RRP42. The rrp42 knock-down mutants mainly displayed variegated and serrated leaves, especially in cauline leaves. The internal anatomy of cauline leaves displayed irregularly shaped palisade cells and a reduced density of mesophyll cells. Interestingly, we detected highly accumulated mRNAs that encode xyloglucan endotransglucosylase/hydrolases (XTHs) and expansins (EXPAs) during later growth stages in rrp42 knock-down mutants. The mRNA decay kinetics analysis for XTH19, EXPA10, and EXPA11 revealed that RRP42 had a role in the decay of these mRNAs in the cytoplasm. RRP42 is localized to both the nucleus and cytoplasm, and RRP42 is preferentially expressed in cauline leaves during later growth stages. Altogether, our results demonstrate that RRP42 is essential for the development of female gametophytes and plays an important role in mesophyll cell morphogenesis.
Highlights
RNA decay is a key step in regulated gene expression
Loss of CSL4 almost had no effects on the integrity or function of the Arabidopsis exosome (Chekanova et al, 2007), and RRP45 is encoded by duplicate genes: RRP45A and RRP45B. rrp45a has no visible defect while rrp45b displayed a reduction of cuticular wax loads on the stem and silique
We used egg cell-specific promoter-controlled CRISPR/Cas9 systems demonstrate that RRP42 is essential for the development of female gametophytes and a homozygous rrp42 mutant is lethal (Figure 1)
Summary
RNA decay is a key step in regulated gene expression. In eukaryotes, the majority of mRNAs undergo decay mainly by a pathway that is initiated by the removal of poly(A)-tail (Couttet et al, 1997; Parker and Song, 2004), and enters one of two irreversible routes: for one, the 5 cap is removed by the decapping complex, after which the mRNA body was degraded from the 5 end by the XRN1 exoribonuclease (Hsu and Stevens, 1993); for another, the unprotected 3 end is attacked by the 3 →5 exonucleases (Garneau et al, 2007; Lange et al, 2009; Christie et al, 2011).The exosome was first identified as a large multisubunit RNase complex that is required for the 3 –5 processing of ribosomal RNA in yeast (Mitchell et al, 1997), and subsequently in archaea (Koonin et al, 2001; Buttner et al, 2005) and other eukaryotes (Allmang et al, 1999b; Chekanova et al, 2002). The six PH-ring subunits show clear structural and sequence similarity to RNases, all of these homologs in the human and yeast exosome are inactive because of lacking important catalytic residues (Liu et al, 2006; Dziembowski et al, 2007), and loss of any individual subunit of the nine is lethal, and causes almost identical profiles of RNA-processing defects (Allmang et al, 1999a,b; Liu et al, 2006). RRP44A, the homolog of Rrp44/Dis, is required for female gametophyte and early embryogenesis (Kumakura et al, 2013). All these data indicate that the subunit of exosome in Arabidopsis probably has different functions for plant growth and development (Lange and Gagliardi, 2010). The functions of other subunits not discussed above are still unclear in Arabidopsis
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