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Roles of the different components of magnesium chelatase in abscisic acid signal transduction.

Du SY, Zhang XF, Lu Z, Xin Q, Wu Z, Jiang T, Lu Y, Wang XF, Zhang DP - Plant Mol. Biol. (2012)

Bottom Line: The overexpression lines of the CHLD gene showed wild-type ABA sensitivity in Arabidopsis.Both the GUN4-RNA interference and overexpression lines of Arabidopsis showed wild-type phenotypes in the major ABA responses.These findings provide clear evidence that the Mg-chelatase-catalyzed Mg-ProtoIX production is distinct from ABA signaling, giving information to understand the mechanism by which the two cellular processes differs at the molecular level.

View Article: PubMed Central - PubMed

Affiliation: MOE Systems Biology and Bioinformatics Laboratory, School of Life Sciences, Tsinghua University, Beijing, China.

ABSTRACT
The H subunit of Mg-chelatase (CHLH) was shown to regulate abscisic acid (ABA) signaling and the I subunit (CHLI) was also reported to modulate ABA signaling in guard cells. However, it remains essentially unknown whether and how the Mg-chelatase-catalyzed Mg-protoporphyrin IX-production differs from ABA signaling. Using a newly-developed surface plasmon resonance system, we showed that ABA binds to CHLH, but not to the other Mg-chelatase components/subunits CHLI, CHLD (D subunit) and GUN4. A new rtl1 mutant allele of the CHLH gene in Arabidopsis thaliana showed ABA-insensitive phenotypes in both stomatal movement and seed germination. Upregulation of CHLI1 resulted in ABA hypersensitivity in seed germination, while downregulation of CHLI conferred ABA insensitivity in stomatal response in Arabidopsis. We showed that CHLH and CHLI, but not CHLD, regulate stomatal sensitivity to ABA in tobacco (Nicotiana benthamiana). The overexpression lines of the CHLD gene showed wild-type ABA sensitivity in Arabidopsis. Both the GUN4-RNA interference and overexpression lines of Arabidopsis showed wild-type phenotypes in the major ABA responses. These findings provide clear evidence that the Mg-chelatase-catalyzed Mg-ProtoIX production is distinct from ABA signaling, giving information to understand the mechanism by which the two cellular processes differs at the molecular level.

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A model for distinction between CHLH- and CHLI-mediated ABA signaling and magnesium (Mg) chelating to protoporphyrin IX (Proto) catalyzed by a CHLH-CHLI-CHLD-GUN4 hetero-tetramer complex. See text for detailed explanation
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Fig8: A model for distinction between CHLH- and CHLI-mediated ABA signaling and magnesium (Mg) chelating to protoporphyrin IX (Proto) catalyzed by a CHLH-CHLI-CHLD-GUN4 hetero-tetramer complex. See text for detailed explanation

Mentions: Taking all the observations together, we propose a working model to explain the difference between the CHLH/CHLI-mediated ABA signaling and function of Mg-chelatase (Fig. 8). In this model, CHLH interacts with CHLI to form a hetero-dimer, which cooperates to regulate ABA signaling, while the function of Mg-chelatase requires all the four components/subunits CHLH, CHLI, CHLD and GUN4 to form a hetero-tetramer complex, which catalyzes magnesium chelating to protoporphyrin IX to produce Mg-ProtoIX. There may exist an equilibrium between the hetero-dimer and hetero-tetramer to meet the needs of two distinct functions, but the chlorophyll biosynthesis may be a privileged process, given that, a low level of the CHLH protein, which could downregulate ABA signaling, may not significantly reduce the chlorophyll contents in leaves (Shen et al. 2006).Fig. 8


Roles of the different components of magnesium chelatase in abscisic acid signal transduction.

Du SY, Zhang XF, Lu Z, Xin Q, Wu Z, Jiang T, Lu Y, Wang XF, Zhang DP - Plant Mol. Biol. (2012)

A model for distinction between CHLH- and CHLI-mediated ABA signaling and magnesium (Mg) chelating to protoporphyrin IX (Proto) catalyzed by a CHLH-CHLI-CHLD-GUN4 hetero-tetramer complex. See text for detailed explanation
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3472068&req=5

Fig8: A model for distinction between CHLH- and CHLI-mediated ABA signaling and magnesium (Mg) chelating to protoporphyrin IX (Proto) catalyzed by a CHLH-CHLI-CHLD-GUN4 hetero-tetramer complex. See text for detailed explanation
Mentions: Taking all the observations together, we propose a working model to explain the difference between the CHLH/CHLI-mediated ABA signaling and function of Mg-chelatase (Fig. 8). In this model, CHLH interacts with CHLI to form a hetero-dimer, which cooperates to regulate ABA signaling, while the function of Mg-chelatase requires all the four components/subunits CHLH, CHLI, CHLD and GUN4 to form a hetero-tetramer complex, which catalyzes magnesium chelating to protoporphyrin IX to produce Mg-ProtoIX. There may exist an equilibrium between the hetero-dimer and hetero-tetramer to meet the needs of two distinct functions, but the chlorophyll biosynthesis may be a privileged process, given that, a low level of the CHLH protein, which could downregulate ABA signaling, may not significantly reduce the chlorophyll contents in leaves (Shen et al. 2006).Fig. 8

Bottom Line: The overexpression lines of the CHLD gene showed wild-type ABA sensitivity in Arabidopsis.Both the GUN4-RNA interference and overexpression lines of Arabidopsis showed wild-type phenotypes in the major ABA responses.These findings provide clear evidence that the Mg-chelatase-catalyzed Mg-ProtoIX production is distinct from ABA signaling, giving information to understand the mechanism by which the two cellular processes differs at the molecular level.

View Article: PubMed Central - PubMed

Affiliation: MOE Systems Biology and Bioinformatics Laboratory, School of Life Sciences, Tsinghua University, Beijing, China.

ABSTRACT
The H subunit of Mg-chelatase (CHLH) was shown to regulate abscisic acid (ABA) signaling and the I subunit (CHLI) was also reported to modulate ABA signaling in guard cells. However, it remains essentially unknown whether and how the Mg-chelatase-catalyzed Mg-protoporphyrin IX-production differs from ABA signaling. Using a newly-developed surface plasmon resonance system, we showed that ABA binds to CHLH, but not to the other Mg-chelatase components/subunits CHLI, CHLD (D subunit) and GUN4. A new rtl1 mutant allele of the CHLH gene in Arabidopsis thaliana showed ABA-insensitive phenotypes in both stomatal movement and seed germination. Upregulation of CHLI1 resulted in ABA hypersensitivity in seed germination, while downregulation of CHLI conferred ABA insensitivity in stomatal response in Arabidopsis. We showed that CHLH and CHLI, but not CHLD, regulate stomatal sensitivity to ABA in tobacco (Nicotiana benthamiana). The overexpression lines of the CHLD gene showed wild-type ABA sensitivity in Arabidopsis. Both the GUN4-RNA interference and overexpression lines of Arabidopsis showed wild-type phenotypes in the major ABA responses. These findings provide clear evidence that the Mg-chelatase-catalyzed Mg-ProtoIX production is distinct from ABA signaling, giving information to understand the mechanism by which the two cellular processes differs at the molecular level.

Show MeSH
Related in: MedlinePlus