An evergreen mind and a heart for the colors of fall

Abstract

With the finest biochemical and molecular approaches, convincing explorative strategies, and long-term vision, Stefan Hörtensteiner succeeded in elucidating the biochemical pathway responsible for chlorophyll degradation. After having contributed to the identification of key chlorophyll degradation products in the course of the past 25 years, he gradually identified and characterized most of the crucial players in the PAO/phyllobilin degradation pathway of chlorophyll. He was one of the brightest plant biochemists of his generation, and his work opened doors to a better understanding of plant senescence, tetrapyrrole homeostasis, and their complex regulation. He sadly passed away on 5 December 2020, aged 57.

Keywords: Chlorophyll catabolism; phyllobilin; plastid; senescence; transporter; vacuole.

Fig. 1.

Overview of the first steps of chlorophyll breakdown. The chemical structure of RP14 (=Hv-NCC-1), the structures of intermediates (Hörtensteiner et al., 2019), and the enzymes that catalyze each step are shown. NCY1 (NON-YELLOW COLORING1)/NOL, CHLOROPHYLL b REDUCTASEs; HCAR, HYDROXYMETHYL CHLOROPHYLL a REDUCTASE; NYE1/SGR (STAY GREEN), MAGNESIUM-DECHELATASE; PPH, PHEOPHYTINASE; PAO, PHEOPHORBIDE A OXYGENASE; RCCR, RCC REDUCTASE; Chl a, chlorophyll a; Chl b, chlorophyll b; HOChl a, hydroxymethyl chlorophyll a; Phein a, pheophytin a; Pheide a, pheophorbide a; RCC, red chlorophyll catabolite; pFCC, primary fluorescent chlorophyll catabolite.

Fig. 2.

Downstream steps of chlorophyll breakdown in angiosperms. CYP89A9, FCC-DEFORMYLASE; TIC55, TRANSLOCON AT THE INNER CHLOROPLAST ENVELOPE 55; MES16, METHYLESTERASE; pFCC, primary fluorescent chlorophyll catabolite; NCC, non-fluorescent chlorophyll catabolite; YCC, yellow chlorophyll catabolite; PiCC, pink chlorophyll catabolite; DFCC, dioxobilin-type fluorescent chlorophyll catabolite; DNCC, dioxobilin-type non-fluorescent chlorophyll catabolite; DYCC, dioxobilin-type yellow chlorophyll catabolite; DPiCC, dioxobilin-type pink chlorophyll catabolite.