A chlorate-resistant mutant defective in the regulation of nitrate reductase gene expression in Arabidopsis defines a new HY locus.

Abstract

Light acts both directly as a signal and indirectly through photosynthesis to regulate the expression of genes encoding nitrate reductase (NR). Here, we report the isolation and characterization of a novel chlorate-resistant mutant that is defective in the regulation of NR gene expression. The response of NR2, but not NR1 or the gene encoding nitrate reductase (NiR), to light signals was impaired in this Arabidopsis mutant, designated cr88. In addition to NR2, the light regulation of the genes encoding the chlorophyll a/b binding protein (CAB) and the small subunit of ribulose bisphosphate carboxylase (RBCS) was also impaired in this mutant. These results suggest that the pathway through which light regulates the expression of NR2, CAB, and RBCS genes is different from those that regulate the expression of NR1 and NiR. An examination of the deetiolation process under different light spectrum showed that cr88 is defective in red light-mediated deetiolation. Complementation tests with various long hypocotyl (hy) mutants indicated that CR88 identifies a new HY locus. The possible functions of CR88 are discussed.

Cosuppression of the chloroplast localized molecular chaperone HSP90.5 impairs plant development and chloroplast biogenesis in Arabidopsis

“…The typical cr88 mutant phenotype is the slower greening process than wild type throughout the life span. For HSP90.5 cosuppression plants, the albino tissues mainly appear in the late developmental stage and never develop in the cotyledons, while cr88 seedlings have yellowish cotyledons [35]. In agreement with this phenotype, we did not observe any significant repression of HSP90.5 expression in cotyledons of the variegated lines by immunoblotting (data not shown).…”

“…By analyzing cr88cop1 double mutant, it was demonstrated that HSP90.5 likely functions downstream of COP1 [36], a master regulator in photomorphogenesis [56]. Impaired expression of photosynthesis-associated genes in the cr88 mutant [35] supports the role of HSP90.5 in photomorphogenesis. However, it is intriguing that HSP90.5 is localized in plastids while all studied photomorphogenesis-related proteins such as COP1, DET1 and photoreceptors [56, 57] are localized in the cytoplasm and nucleus.…”

Genome-wide analysis of the Populus Hsp90 gene family reveals differential expression patterns, localization, and heat stress responses

“…The conserved organelle localization of Hsp90 implies that they might play roles in organelle-specific development or stress response. It has been suggested that mutation of the chloroplast-localized AtHsp90-5 causes altered response to red light, chlorate resistance and constitutively delayed chloroplast development in the cr88 mutant [13,31,32]. In animals, a mitochondrial-localized Hsp90 appeared to have a critical role in cell cycle progression, cellular differentiation, and apoptosis [33,34].…”

Structure, Function, and Regulation of the Hsp90 Machinery

“…cHsp90 has attracted less attention in the past, although it has an essential function in plant development (Inoue et al 2013). One of the major roles of cHsp90 is associated with protein import into the organelle (Li and Chiu 2010;Flores-Pérez and Jarvis 2013;Inoue et al 2013) and the maturation of photosynthesisrelated proteins (Lin and Cheng 1997;Cao et al 2000). Importantly, in Chlamydomonas reinhardtii, a "foldosome" has been identified composed of Hsp90C, Hsp70B, the chloroplast DnaJ homolog CDJ1, and the chloroplast GrpE homolog CGE1, representing orthologs of cytosolic Hsp90, Hsp70, Hsp40, and the Hsp70 nucleotide exchange factor GrpE (Willmund and Schroda 2005;Willmund et al 2008).…”