The C-terminal cysteine-rich motif of NYE1/SGR1 is indispensable for its function in chlorophyll degradation in Arabidopsis

Abstract

KEY MESSAGE The C-terminal cysteine-rich motif of NYE1/SGR1 affects chlorophyll degradation likely by mediating its self-interaction and conformational change, and somehow altering its Mgdechelating activity in response to the changing redox potential. During green organ senescence in plants, the most prominent phenomenon is the degreening caused by net chlorophyll (Chl) loss. NON-YELLOWING1/STAY-GREEN1 (NYE1/SGR1) was recently reported to be able to dechelates magnesium (Mg) from Chl a to initiate its degradation, but little is known about the domain/motif basis of its functionality. In this study, we carried out a protein truncation assay and identified a conserved cysteinerich motif (CRM, P-X3-C-X3-C-X-C2-F-P-X5-P) at its C terminus, which is essential for its function. Genetic analysis showed that all four cysteines in the CRM were irreplaceable, and enzymatic assays demonstrated that the mutation of each of the four cysteines affected its Mg-dechelating activity. The CRM plays a critical role in the conformational change and self-interaction of NYE1 via the formation of inter-and intra-molecular disulfide bonds. Our results may provide insight into how NYE1 responds to rapid redox changes during leaf senescence and in response to various environmental stresses.

Roles of stay-green (SGR) homologs during chlorophyll degradation in green plants

“…SGR possesses a cysteine rich motif (CRM, P-X3-C-X3C-X-C2-F-P-X5-P), which is indispensable for Mg-dechelatase (Fig. 1 b, motif6) (Xie et al 2019 ), but there is not such motif in SGRL. Within the CRM motif, four cysteine residues are reported to participate in inter- or intramolecular crosslinking or in redox regulation.…”

Autophagy-Related 2 Regulates Chlorophyll Degradation under Abiotic Stress Conditions in Arabidopsis

“…The chlorophyll cycle, including chlorophyll synthesis and chlorophyll degradation, is strictly regulated over the plant life period [ 6 , 7 , 8 ]. In Arabidopsis , the chlorophyll biosynthesis pathway contains 15 key enzymes encoded by 27 genes [ 9 ].…”

Defect in Brnym1, a magnesium-dechelatase protein, causes a stay-green phenotype in an EMS-mutagenized Chinese cabbage (Brassica campestris L. ssp. pekinensis) line

“…The latter is essential for SGR activity in Chl degradation. The extra benzene ring in the mutant might obstruct disulfide bond formation and suppress mg dechelation 33 . In fact, we observed that magnesium-dechelatase activity was significantly downregulated in the mutant.…”

“…Matsuda et al (2016) showed that the SGR/NYE function in unicellular algae is conserved in higher plants 37 . The Cterminal domain of NYE1 212-242 has a CRM and is vital to SGR function in Chl degradation 33 . However, several unresolved issues merit investigation: (a) the mechanism by which stay-green plants avoid damage from pigment accumulation if certain chlorophyll metabolic intermediates are photosensitizers; (b) the nutritional quality of stay-green Chinese cabbage compared with that of the wild type; (c) whether the stay-green mutation also conserves mineral nutrients and photosynthate; (d) whether endogenous phytohormones affect the stay-green mutant; and (e) postharvest longevity in the mutant compared with that in the wild type.…”

“…The magnesium-dechelatase catalyzes the first step of Chl a degradation 32 . The Cterminal domain of NYE1/SGR contains a cysteine-rich motif (CRM) essential for SGR function in Chl degradation, mg dechelation, and conformational changes in SGR via disulfide bond formation 33 .…”