NAI1 Gene Encodes a Basic-Helix-Loop-Helix–Type Putative Transcription Factor That Regulates the Formation of an Endoplasmic Reticulum–Derived Structure, the ER Body

Abstract

Plant cells develop various types of endoplasmic reticulum (ER)-derived structures with specific functions. ER body, an ERderived compartment in Arabidopsis thaliana, is a spindle-shaped structure. The NAI1 gene regulates the development of ER bodies because mutation of NAI1 abolishes the formation of ER bodies. To better understand the role of NAI1, we cloned the NAI1 gene using a positional cloning strategy. The nai1-1 mutant had a single nucleotide change at an intron acceptor site of At2g22770 (NAI1 gene). Because of this mutation, aberrant splicing of NAI1 mRNA occurs in the nai1-1 mutant. NAI1 encodes a transcription factor that has a basic-helix-loop-helix (bHLH) domain. Transient expression of NAI1 induced ER bodies in the nai1-1 mutant. Two-dimensional electrophoresis and RT-PCR analyses showed that a putative lectin was depressed at both the mRNA and protein levels in nai1 mutants, as was a b-glucosidase (PYK10). Our results provide direct evidence that a bHLH protein plays a role in the formation of ER bodies.

Dynamic Proteomics Emphasizes the Importance of Selective mRNA Translation and Protein Turnover during Arabidopsis Seed Germination

“…Indeed, PBP1 contributes to PYK10 activity and may act as a molecular chaperone that facilitates the correct polymerization of PYK10 when cells are exposed to stress. The PYK10 and PBP1 genes are both regulated by the NAI1 (At2g22770) basic-helix-loop-helix-type transcription factor (105). Moreover, it has also been demonstrated that NAI2 (At3g15950) deficiency in Arabidopsis specifically reduces the accumulation of PYK10 protein but does not affect the accumulation of PBP1 (111).…”

“…The Arabidopsis PYK10 protein (At3g09260) was described as a root-and hypocotyl-specific myrosinase (104) whose activity could release glucose and breakdown products, including defense compounds such as isothiocyanates. To date, the physiological role and natural substrate(s) of PYK10 are unknown, but functional ␤-glucosidase and ␤-fucosidase activities have been reported for PYK10 (105). In addition, nitrile-specifier protein 2 is abundant in both dry and germinating Arabidopsis seeds and is also progressively translated (supplemental Tables S1 and S7).…”

KATAMARI1/MURUS3 Is a Novel Golgi Membrane Protein That Is Required for Endomembrane Organization in Arabidopsis

“…Several groups have used GFP-based screens to isolate Arabidopsis mutants that have abnormally shaped organelles, including mitochondria (Logan et al, 2003), peroxisomes (Mano et al, 2004), vacuolar membranes (Avila et al, 2003), and ER bodies (Matsushima et al, 2003(Matsushima et al, , 2004. Thus, GFP screening is a useful method for studying organelle morphology and biogenesis.…”

“…Arabidopsis plants (1 to 3 weeks old) were transformed with each chimeric gene by particle bombardment as described previously (Matsushima et al, 2004). To generate transgenic Arabidopsis plants, we transformed kam1-1 with a chimeric gene encoding KAM1-mRFP by the in planta method (Bechtold and Pelletier, 1998).…”

Soybean SAT1 ( Symbiotic Ammonium Transporter 1 ) encodes a bHLH transcription factor involved in nodule growth and NH 4 + transport

“…S5). In Arabidopsis, a bHLHm1 homolog, At2g22770 (NAI1), is involved in stress-induced synthesis of ER bodies in root and leaf tissues (42). It is possible that bHLHm1 TFs may have a role in facilitating other microbial interactions, including pathogen responses or mycorrhizal symbioses, both of which involve C supply from the plant.…”