A genetic link between epigenetic repressor AS1-AS2 and a putative small subunit processome in leaf polarity establishment of Arabidopsis.

Yoko Matsumura,Ayami Nakagawa,Manuel Echeverria,Julio Saéz-Vásquez,Hiro Takahashi,Munetaka Sugiyama,Kenzo Nakamura,Nanako Ishibashi,Shoko Kojima,Yasunori Machida,Iwai Ohbayashi,Chiyoko Machida,Rika Hayashi,Sumie Keta

doi:10.1242/bio.019109

Yoko Matsumura, Ayami Nakagawa + Show 12 more

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https://doi.org/10.1242/bio.019109

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ABSTRACTAlthough the DEAD-box RNA helicase family is ubiquitous in eukaryotes, its developmental role remains unelucidated. Here, we report that cooperative action between the Arabidopsis nucleolar protein RH10, an ortholog of human DEAD-box RNA helicase DDX47, and the epigenetic repressor complex of ASYMMETRIC-LEAVES1 (AS1) and AS2 (AS1-AS2) is critical to repress abaxial (ventral) genes ETT/ARF3 and ARF4, which leads to adaxial (dorsal) development in leaf primordia at shoot apices. Double mutations of rh10-1 and as2 (or as1) synergistically up-regulated the abaxial genes, which generated abaxialized filamentous leaves with loss of the adaxial domain. DDX47 is part of the small subunit processome (SSUP) that mediates rRNA biogenesis. In rh10-1 we found various defects in SSUP-related events, such as: accumulation of 35S/33S rRNA precursors; reduction in the 18S/25S ratio; and nucleolar hypertrophy. Double mutants of as2 with mutations of genes that encode other candidate SSUP-related components such as nucleolin and putative rRNA methyltransferase exhibited similar synergistic defects caused by up-regulation of ETT/ARF3 and ARF4. These results suggest a tight link between putative SSUP and AS1-AS2 in repression of the abaxial-determining genes for cell fate decisions for adaxial development.

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A step of developmental events in multicellular organisms is characterized by the activation of a new genetic program and the inactivation of the previous program, which is mostly mediated by epigenetic systems
A novel enhancer mutation of as2 that causes adaxial defects of leaves is present in the gene for DEAD-box-type RNA helicase RNA HELICASE10 (RH10) We found the strong enhancer mutant in our library of mutagenized seeds of as2-1 (Kojima et al, 2011; Ishibashi et al, 2012), which showed filamentous and trumpet-like leaves and was named enhancer of asymmetric leaves two
Molecular and genetic analyses showed that east2 was a recessive single mutation in the 9th exon in At5g60990, which is predicted to encode a protein belonging to the DEAD-box RNA helicase family called RNA HELICASE10 (RH10) (Fig. S1A-D) (Aubourg et al, 1999)

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A step of developmental events in multicellular organisms is characterized by the activation of a new genetic program and the inactivation of the previous program, which is mostly mediated by epigenetic systems. Received 30 April 2016; Accepted 25 May 2016 proteins ASYMMETRIC LEAVES1 (AS1) and ASYMMETRIC LEAVES2 (AS2) (AS1-AS2) of Arabidopsis thaliana has been proposed to play a role in the epigenetic silencing involved in early leaf development from stem cells at the shoot apices (Phelps-Durr et al, 2005; Guo et al, 2008; Lodha et al, 2013; Iwasaki et al, 2013) Both nuclear proteins are localized as speckles, called AS2 bodies, to regions adjacent to and sometimes inside the nucleolus (Ueno et al, 2007; Luo et al, 2012a), suggesting a potential role of AS1 and AS2 in the gene silencing through nucleolus-associated events. KANADI genes ( parts of abaxial genes) directly repress AS2 ( part of adaxial genes) transcription (Wu et al, 2008)

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