Induction of isoforms of tetrapyrrole biosynthetic enzymes, AtHEMA2 and AtFC1, under stress conditions and their physiological functions in Arabidopsis.
In the tetrapyrrole biosynthetic pathway, isoforms of glutamyl-tRNA reductase (HEMA2) and ferrochelatase1 (FC1) are mainly expressed in nonphotosynthetic tissues. Here, using promoter-beta-glucuronidase constructs, we showed that the expressions of Arabidopsis (Arabidopsis thaliana) HEMA2 (AtHEMA2) and FC1 (AtFC1) were induced in photosynthetic tissues by oxidative stresses such as wounding. Transcript levels and beta-glucronidase activity were rapidly induced within 30 min, specifically in the wound area in a jasmonate-independent manner. Transcriptome analysis of wound-specific early inducible genes showed that AtHEMA2 and AtFC1 were coinduced with hemoproteins outside plastids, which are related to defense responses. Ozone fumigation or reagents generating reactive oxygen species induced the expression of both genes in photosynthetic tissues, suggesting that reactive oxygen species is involved in the induction. Since cycloheximide or puromycin induced the expression of both genes, inhibition of cytosolic protein synthesis is involved in the induction of these genes in photosynthetic tissues. The physiological functions of AtHEMA2 and AtFC1 were investigated using insertional knockout mutants of each gene. Heme contents of the roots of both mutants were about half of that of the respective wild types. In wild-type plants, heme contents were increased by ozone exposure. In both mutants, reduction of the ozone-induced increase in heme content was observed. These results suggest the existence of the tetrapyrrole biosynthetic pathway controlled by AtHEMA2 and AtFC1, which normally functions for heme biosynthesis in nonphotosynthetic tissues, but is induced in photosynthetic tissues under oxidative conditions to supply heme for defensive hemoproteins outside plastids.
Nagai
Satoshi
S
Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8501, Japan.
Koide
Masumi
M
Takahashi
Shigekazu
S
Kikuta
Akihiro
A
Aono
Mitsuko
M
Sasaki-Sekimoto
Yuko
Y
Ohta
Hiroyuki
H
Takamiya
Ken-ichiro
K
Masuda
Tatsuru
T
D000222:Adaptation, Physiological; D000445:Aldehyde Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D005294:Ferrochelatase / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D006418:Heme / Q000378:metabolism; D006420:Hemeproteins / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D016254:Mutagenesis, Insertional; D018384:Oxidative Stress / Q000502:physiology; D010126:Ozone / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D045725:Tetrapyrroles / Q000096:biosynthesis*
D006420:Hemeproteins; D007527:Isoenzymes; D017382:Reactive Oxygen Species; D045725:Tetrapyrroles; D006418:Heme; D010126:Ozone; D000445:Aldehyde Oxidoreductases; C067282:glutamyl tRNA reductase; D005294:Ferrochelatase