AtRH57, a DEAD‐box RNA helicase, is involved in feedback inhibition of glucose‐mediated abscisic acid accumulation during seedling development and additively affects pre‐ribosomal RNA processing with high glucose

Abstract

The Arabidopsis thalianaT-DNA insertion mutant rh57-1 exhibited hypersensitivity to glucose (Glc) and abscisic acid (ABA). The other two rh57 mutants also showed Glc hypersensitivity similar to rh57-1, strongly suggesting that the Glc-hypersensitive feature of these mutants results from mutation of AtRH57. rh57-1 and rh57-3 displayed severely impaired seedling growth when grown in Glc concentrations higher than 3%. The gene, AtRH57 (At3g09720), was expressed in all Arabidopsis organs and its transcript was significantly induced by ABA, high Glc and salt. The new AtRH57 belongs to class II DEAD-box RNA helicase gene family. Transient expression of AtRH57-EGFP (enhanced green fluorescent protein) in onion cells indicated that AtRH57 was localized in the nucleus and nucleolus. Purified AtRH57-His protein was shown to unwind double-stranded RNA independent of ATP in vitro. The ABA biosynthesis inhibitor fluridone profoundly redeemed seedling growth arrest mediated by sugar. rh57-1 showed increased ABA levels when exposed to high Glc. Quantitative real time polymerase chain reaction analysis showed that AtRH57 acts in a signaling network downstream of HXK1. A feedback inhibition of ABA accumulation mediated by AtRH57 exists within the sugar-mediated ABA signaling. AtRH57 mutation and high Glc conditions additively caused a severe defect in small ribosomal subunit formation. The accumulation of abnormal pre-rRNA and resistance to protein synthesis-related antibiotics were observed in rh57 mutants and in the wild-type Col-0 under high Glc conditions. These results suggested that AtRH57 plays an important role in rRNA biogenesis in Arabidopsis and participates in response to sugar involving Glc- and ABA signaling during germination and seedling growth.

Master regulators in plant glucose signaling networks

“…Extensive genetic, molecular, cellular, and biochemical analyses have uncovered the intimate links between HXK1-mediated glucose signaling and multiple hormones, including but not limited to ethylene, abscisic acid (ABA), auxin and cytokinin (Rolland et al, 2002; Leon and Sheen, 2003; Moore et al, 2003; Yanagisawa et al, 2003; Rolland et al, 2006; Huang et al, 2008; Ramon et al, 2008; Cho et al, 2010; Karve et al, 2012; Hsu et al, 2014). In maize and Arabidopsis leaf cells, Arabidopsis HXK1 but not the yeast HXK promotes the proteasome-dependent degradation of nuclear EIN3 (ETHYLENE INSENSITIVE3) and EIL1 (EIN3-LIKE1) through the C-terminus, which is stabilized by ethylene.…”

“…Consistently, ein3 as well as etr1, ein2 and mkk9 are hypersensitive to glucose but insensitive to ethylene (Yanagisawa et al, 2003; Yoo et al, 2008). HXK1 also modulates the glucose repression of ERF1 (ETHYLENE RESPONSE FACTOR1) in ethylene signaling, and the glucose activation of ABA2 in ABA synthesis and ABI4 / ABI5 ( ABA INSENSITIVE ) transcription factors in ABA signaling (Rolland et al, 2002; Leon and Sheen, 2003; Rolland et al, 2006; Ramon et al, 2008; Cho et al, 2010; Hsu et al, 2014). More detailed molecular mechanisms underlying sugar regulation of hormonal signaling and biosynthesis remained to be further resolved using defined HXK1 mutants, as distinct signaling and metabolic effects of sugars may be involved (Moore et al, 2003; Ohto et al, 2006; Loreti et al, 2008; Mishra et al, 2009; Mudgil et al, 2009; LeClere et al, 2010; Lin et al, 2010).…”

Mechanism of Cytoplasmic mRNA Translation

“…Plants have comparable RNA helicases (Bush et al, 2009), but their role in plant translation has not been elucidated and they may also have other specific roles in post-transcriptional processes. For example, the nuclear-localized AteIF4AIII was shown to function in nuclear pre-mRNA/mRNA movement during hypoxia (Koroleva et al, 2009a;Koroleva et al, 2009b) and the DEAD box helicase AtRH57 appears to be involved in rRNA processing in response to glucose and abscisic acid (Hsu et al, 2013).…”

atBRX1-1 and atBRX1-2 are involved in an alternative rRNA processing pathway in Arabidopsis thaliana

“…Sucrose density gradients were performed as described (Hsu et al 2014) because we observed inefficient release of nucleolar preribosomes using our standard procedure (Missbach et al 2013;Weis et al 2014). Total cell lysate from A. thaliana cell culture was separated on a 10%-40% (w/v) sucrose gradient by centrifugation for 18 h at 100,000g in a TST41.14 rotor.…”