Tetrapyrrole Metabolism inArabidopsis thaliana

Abstract

This manuscript is dedicated to Prof. Mamoru Mimuro of Kyoto University who passed away in Februay 2011.Higher plants produce four classes of tetrapyrroles, namely, chlorophyll (Chl), heme, siroheme, and phytochromobilin. In plants, tetrapyrroles play essential roles in a wide range of biological activities including photosynthesis, respiration and the assimilation of nitrogen/sulfur. All four classes of tetrapyrroles are derived from a common biosynthetic pathway that resides in the plastid. In this article, we present an overview of tetrapyrrole metabolism in Arabidopsis and other higher plants, and we describe all identified enzymatic steps involved in this metabolism. We also summarize recent findings on Chl biosynthesis and Chl breakdown. Recent advances in this field, in particular those on the genetic and biochemical analyses of novel enzymes, prompted us to redraw the tetrapyrrole metabolic pathways. In addition, we also summarize our current understanding on the regulatory mechanisms governing tetrapyrrole metabolism. The interactions of tetrapyrrole biosynthesis and other cellular processes including the plastid-to-nucleus signal transduction are discussed.

Different Mechanisms Are Responsible for Chlorophyll Dephytylation during Fruit Ripening and Leaf Senescence in Tomato

“…However, demonstration that chloroplast-localized PAO, acting downstream of dephytylation, is involved in chlorophyll breakdown (Hörtensteiner et al, 1995;Sakuraba et al, 2012) and the finding that the absence of both Arabidopsis CLHs had only a marginal effect on chlorophyll breakdown challenged this idea and questioned whether CLHs are involved at all. The identification of PPH as a pheophytin-specific phytol hydrolase ) supported this view, and now it is commonly accepted that PPHs rather than CLHs are responsible for leaf senescence-related chlorophyll breakdown (Tanaka et al, 2011), at least in Arabidopsis and rice. The results of this study extend this assumption to tomato, because, as in Arabidopsis pph mutants , leaf yellowing was largely blocked in SlPPH-silencing lines and significant amounts of pheophytin a accumulated upon senescence induction in the dark (Fig.…”

“…Except for the activity that is responsible for magnesium dechelation, genes encoding these catalytic activities have been identified in Arabidopsis (Arabidopsis thaliana) and other species. Since all except one of the phyllobilins that have been characterized structurally are derived from chlorophyll a (Hörtensteiner and Kräutler, 2011), the reductive part of the chlorophyll cycle that converts chlorophyll b into chlorophyll a has been considered an integral part of senescence-related chlorophyll breakdown (Tanaka et al, 2011).…”

Ethylene-orchestrated circuitry coordinates a seedling’s response to soil cover and etiolated growth

“…HEMA1 is known to encode the first committed enzyme of the chlorophyll biosynthesis pathway of higher land plants (Fig. 6A) (51)(52)(53), whereas genomes uncoupled 4/5 (GUN4/GUN5) are known to determine the branch pathways leading to Pchlide/chlorophyll synthesis (54)(55)(56). As a result of chlorophyll synthesis occurring in the dark, a pool of Pchlide accumulates in the etioplasts.…”

Phosphorylation of GENOMES UNCOUPLED 4 Alters Stimulation of Mg Chelatase Activity in Angiosperms

“…Chelation of Mg 2+ is catalyzed by the ATP-consuming Mg chelatase (MgCh), which consists of the three subunits CHLH, CHLD, and CHLI, with the H-subunit binding the substrate (Fuesler et al, 1981;Walker and Weinstein, 1991;Gibson et al, 1999;Gräfe et al, 1999;Jensen et al, 1999;Karger et al, 2001;Lundqvist et al, 2010;Chen et al, 2015a). To prevent the accumulation of free and phototoxic metabolic intermediates, TBS is subject to tight transcriptional and posttranslational control in response to endogenous and environmental stimuli (Mochizuki et al, 2010;Tanaka et al, 2011;Brzezowski et al, 2015). Posttranslational control of TBS involves multiple mechanisms, including assembly of biand multi-molecular protein complex and redox control (Stenbaek and Jensen, 2010;Czarnecki and Grimm, 2013;.…”