At RH57, 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.

The Arabidopsis thaliana T- 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 At RH57. rh57-1 and rh57-3 displayed severely impaired seedling growth when grown in Glc concentrations higher than 3%. The gene, At RH57 ( At3g09720), was expressed in all Arabidopsis organs and its transcript was significantly induced by ABA, high Glc and salt. The new At RH57 belongs to class II DEAD-box RNA helicase gene family. Transient expression of At RH57- EGFP (enhanced green fluorescent protein) in onion cells indicated that At RH57 was localized in the nucleus and nucleolus. Purified At RH57- 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 At RH57 acts in a signaling network downstream of HXK1. A feedback inhibition of ABA accumulation mediated by At RH57 exists within the sugar-mediated ABA signaling. At RH57 mutation and high Glc conditions additively caused a severe defect in small ribosomal subunit formation. The accumulation of abnormal pre-r RNA 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 At RH57 plays an important role in r RNA biogenesis in Arabidopsis and participates in response to sugar involving Glc- and ABA signaling during germination and seedling growth. [ABSTRACT FROM AUTHOR]