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Published on April 6, 2007; 10.1104/pp.107.100065

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Received March 23, 2007
Accepted March 28, 2007

Induction of Isoforms of Tetrapyrrole Biosynthetic Enzymes, atHEMA2 and atFC1, under Stress Conditions and their Physiological Functions in Arabidopsis

Satoshi Nagai , Masumi Koide , Shigekazu Takahashi , Akihiro Kikuta , Mitsuko Aono , Yuko Sasaki-Sekimoto , Hiroyuki Ohta , Ken-ichiro Takamiya , and Tatsuru Masuda *

Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8501, Japan; Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan; Environmental Biology Division, National Institute for Environmental Studies, Tsukuba 305-8506 Japan

* Corresponding author; email: ctmasuda{at}mail.ecc.u-tokyo.ac.jp.

In the tetrapyrrole biosynthetic pathway, isoforms of glutamyl-tRNA reductase (HEMA2) and ferrochelatase (FC1) are mainly expressed in non-photosynthetic tissues. Here, using promoter-GUS constructs, we showed that the expressions of Arabidopsis HEMA2 (atHEMA2) and FC1 (atFC1) were induced in photosynthetic tissues by oxidative stresses, such as wounding. Transcript levels and GUS 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 co-induced 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 non-photosynthetic tissues, but is induced in photosynthetic tissues under oxidative conditions to supply heme for defensive hemoproteins outside plastids.




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M. Moulin, A. C. McCormac, M. J. Terry, and A. G. Smith
Tetrapyrrole profiling in Arabidopsis seedlings reveals that retrograde plastid nuclear signaling is not due to Mg-protoporphyrin IX accumulation
PNAS, September 30, 2008; 105(39): 15178 - 15183.
[Abstract] [Full Text] [PDF]


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