Biology subjects

Hani, U.

Publications and source records attributed to Hani, U..

2 recordsLinked to original sources

bioRxiv2025

The EGY1-SGR1 module controls chloroplast development and senescence by modulating photosynthetic functions

The chloroplast plays essential roles not only in production of biochemical energy and metabolism, but also in plant development, including senescence. We describe a mutant with an unusual progression of senescence and identify it as an allele of ethylene-dependent gravitropism-deficient and yellow-green 1 (egy1-5). EGY1 encodes a chloroplast-localized metalloprotease that regulates chlorophyll metabolism. The single egy1-5 mutant exhibits defects in various aspects of chloroplast function, including abnormal accumulation of photosynthetic complexes, defects in photosynthetic electron transfer chain and altered responses to the chemicals methyl viologen and lincomycin. Additionally, egy1 lacks guard cell chloroplasts. We performed a suppressor mutant screen in the egy1 background to identify new regulators of senescence and chloroplast development. We found two suppressors that restored green leaves and mapping revealed that both suppressors had mutations in STAY-GREEN 1 (SGR1). SGR1 encodes the Mg2+ dechelatase enzyme, which catalyses the first step in chlorophyll breakdown. Several defects in the egy1 mutant were either fully or partially suppressed in egy1 sgr1. This enabled the function of EGY1 to be isolated, independent of the pleiotropic effects of chlorophyll degradation. Our findings suggest that chlorophyll homeostasis regulates the overall development and function of the chloroplast as well as plant senescence. HighlightIdentifying new mutants with defects in chlorophyll metabolism and chloroplast development shows that proper chlorophyll homeostasis is necessary for maintaining functional chloroplasts.

plant biology↗

bioRxiv2023

A complex and dynamic redox network regulating oxygen reduction at photosystem I

Thiol-dependent redox regulations of enzyme activities play a central role in regulating photosynthesis. Beside the regulation of metabolic pathways, alternative electron transport has been shown to be subjected to thiol-dependent regulation. We investigated the regulation of O2 reduction at photosystem I. The level of O2 reduction in leaves and isolated thylakoid membranes depends on the photoperiod in which plants are grown. We used a set of Arabidopsis mutant plants affected in the stromal, membrane and lumenal thiol network to study the redox protein partners involved in regulating O2 reduction. Light-dependent O2 reduction was determined in leaves and in thylakoids of plants grown in short day and long day conditions using a spin-trapping EPR assay. In wild type samples from short day, ROS generation was twice the amount of that in samples from long day, while this difference was abolished in several redoxin mutants. An in vitro reconstitution assays showed that thioredoxin m, NADPH-dependent reductase C (NTRC) and NADPH are required for high O2 reduction levels in long day thylakoids. Using isolated photosystem I, we also show that reduction of a PSI protein is responsible for the increase in O2 reduction. Furthermore, differences in the membrane localization of thioredoxins m and 2-Cys peroxiredoxin were demonstrated between thylakoids of short day and long day plants. Finally, we propose a model of redox regulation of O2 reduction according to the reduction power of the stroma and the capabilities of the different thiol-containing proteins to form a network of redox interactions.

biochemistry↗