Biology subjects

Belcher, S.

Publications and source records attributed to Belcher, S..

5 recordsLinked to original sources

bioRxiv2024

Opposing action of photosystem II assembly factors RBD1 and HCF136 underlies light-regulated psbA translation in plant chloroplasts

The D1 reaction center protein of photosystem II (PSII) is subject to light-induced damage. In plants, D1 photodamage activates translation of the chloroplast psbA mRNA encoding D1, providing D1 for PSII repair. Genetic data have implicated three D1 assembly factors in the regulatory mechanism: HCF244 and RBD1 activate psbA translation whereas HCF136 represses psbA translation in the dark. To clarify the regulatory circuit, we analyzed psbA ribosome occupancy in dark-adapted and illuminated rbd1 and hcf136;rbd1 double mutants in Arabidopsis, and in Zm-hcf244 and Zm-hcf136;Zm-hcf244 double mutants in maize. The results show that RBD1 is required for the light-induced recruitment of ribosomes to psbA mRNA but has little effect on psbA ribosome occupancy in the dark. Furthermore, RBD1 is dispensable for psbA translation when HCF136 is absent, indicating that RBD1 activates psbA translation indirectly, by inhibiting HCF136s repressive effect. By contrast, HCF244 is required to recruit ribosomes to psbA mRNA in light, dark, and in the absence of HCF136. These results demonstrate that the step in D1 assembly that is mediated by RBD1 is central to the perception of the D1 photodamage that triggers D1 synthesis, that RBD1 activates psbA translation in the light by relieving the repressive effect of an HCF136-dependent assembly intermediate, and that HCF244 acts independently of these events to activate psbA translation. The results implicate a feature of nascent D1 that is affected by both HCF136 and RBD1 as the signal that reports D1 photodamage to regulate psbA translation rate as needed for PSII repair. Significance StatementThe D1 subunit of photosystem II (PSII) is damaged by light and must be replaced with nascent D1 to maintain photosynthesis. In plants, D1 photodamage triggers D1 synthesis by activating translation of chloroplast psbA mRNA encoding D1. Our results demonstrate that an antagonistic interplay between two photosystem II assembly factors, HCF136 and RBD1, is at the core of the signal transduction process that senses light-induced D1 damage to regulate psbA translation. These findings implicate a feature of nascent D1 that is affected by both HCF136 and RBD1 as the signal that reports D1 photodamage to tune psbA translation as needed for PSII repair. The results elucidate an assembly-coupled translational rheostat that maintains photosynthesis in the face of PSII photodamage.

plant biology↗

bioRxiv2024

Light activates psbA translation in plants by relieving inhibition of translation factor HCF173 by the psbA ORF in cis

The D1 reaction center protein of photosystem II is subject to photooxidative damage. Photodamaged D1 must be replaced with newly synthesized D1 to maintain photosynthesis. In plant chloroplasts, D1 synthesis is coupled to D1 photodamage via regulated translation initiation on psbA mRNA, which encodes D1. Mechanisms underlying this coupling are unclear. We show by analysis of reporter constructs in tobacco that the psbA translational activators HCF173 and HCF244 activate via cis-elements in the psbA UTRs and that the 5 UTR sequence bound by HCF173 is essential for psbA expression. However, the psbA UTRs are not sufficient to program light-regulated translation. Instead, the psbA open reading frame acts in cis to repress translation initiation, and D1 photodamage relieves this repression. A truncated HCF173 mutant conditions constitutively high psbA ribosome occupancy in the dark, implicating HCF173 as a mediator of the repressive signal. We propose a model that is informed by structures of the Complex I assembly factor CIA30/NDUFAF1 positing that D1 photodamage relieves a repressive cotranslational interaction between nascent D1 and HCF173s CIA30 domain, and that the D1 assembly factor HCF136 promotes this interaction. These findings elucidate a translational rheostat that maintains photosynthesis in the face of inevitable photosystem II photodamage.

plant biology↗

bioRxiv2022

Correlated retrograde and developmental regulons implicate multiple retrograde signals as coordinators of chloroplast development in maize

Signals emanating from chloroplasts influence nuclear gene expression, but roles of retrograde signals during chloroplast development are unclear. To address this gap, we analyzed transcriptomes of four non-photosynthetic maize mutants and interpreted them in the context of transcriptome dynamics during normal leaf development. We analyzed two albino mutants lacking plastid ribosomes and two chlorotic mutants with thylakoid targeting or plastid transcription defects. The [~]2700 differentially expressed genes fall into six major categories based on the polarity and mutant-specificity of the change. These distinct retrograde responses correlate with distinct developmental dynamics, with down-regulated genes expressed later in normal development and up-regulated genes acting early. Photosynthesis genes are down-regulated specifically in the albino mutants, whereas up-regulated genes are enriched for functions in chloroplast biogenesis and cytosolic translation. TOR signaling is elevated in plastid ribosome-deficient mutants and declines in concert with plastid ribosome buildup during leaf development. Our results implicate three plastid signals as integral players during photosynthetic differentiation. One signal requires plastid ribosomes and activates photosynthesis genes. A second signal reflects attainment of chloroplast maturity and represses chloroplast biogenesis genes. A third signal responds to nutrient consumption by developing chloroplasts and represses TOR, which down-regulates cell proliferation genes early in leaf development. One sentence summaryTranscriptomes of non-photosynthetic maize mutants when interpreted in the context of normal developmental dynamics implicate three plastid signals as coordinators of photosynthetic differentiation. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (https://academic.oup.com/plcell/pages/General-Instructions) is Alice Barkan (abarkan@uoregon.edu)

plant biology↗

bioRxiv2017

Effects of Bisphenol A on Incidence and Severity of Cardiac Lesions in the NCTR-Sprague-Dawley Rat: A CLARITY-BPA Study

The goal of this study was to determine whether bisphenol A (BPA) had adverse effects indicative of cardiac toxicity. As part of the \"Consortium Linking Academic and Regulatory Insights on BPA Toxicity\" (CLARITY-BPA), study dams and offspring were exposed by daily gavage to five doses of BPA ranging from 2.5 to 25000 g/kg/day, 0.05 or 0.5 g/kg/day 17-ethinyl-estradiol (EE) or 0.3% carboxymethylcellulose vehicle. Exposure-related effects were analyzed in isolated hearts by quantitative morphometry and histopathology. No dose-related changes in body weight were detected. Across all exposure groups including vehicle controls, body weight of continuously dosed males was reduced compared to males dosed only until PND21. Heart weight was increased only in females exposed to EE, and consistent alterations in LV wall thickness were not observed. Exposure-related changes in collagen accumulation were minor and limited to highest EE exposure groups with increased collagen accumulation in PND21 males. Decreased collagen was observed in hearts of BPA or EE exposed females at PND90 and PND180. In BPA or EE treated females cardiomyopathy incidence and severity was significantly increased compared to control females at PND21 with myocardial degeneration observed in both males and females at PND21 and PND90.

pharmacology and toxicology↗

bioRxiv2017

Impacts of Bisphenol A and Ethinyl Estradiol on Male and Female CD-1 Mouse Spleen

The endocrine disruptor bisphenol A (BPA) and the pharmaceutical 17-ethinyl estradiol (EE) are synthetic chemicals with estrogen-like activities. Despite ubiquitous human exposure to BPA, and the wide-spread clinical use of EE as oral contraceptive adjuvant, the impact of these estrogenic endocrine disrupting chemicals (EDCs) on the immune system is unclear. Here we report results of in vivo dose response studies that analyzed the histology and microstructural changes in the spleen of adult male and female CD-1 mice exposed to 4 to 40,000 g/kg/day BPA or 0.02 to 2 g/kg/day EE from conception until 12-14 weeks of age. Results of that analysis indicate that both BPA and EE have dose- and sex-specific impacts on the cellular and microanatomical structures of the spleens that reveal minor alterations in immunomodulatory and hematopoietic functions. These findings support previous studies demonstrating the murine immune system as a sensitive target for estrogens, and that oral exposures to BPA and EE have important estrogen-like immunomodulatory affects in both sexes of the CD-1 mouse.

pharmacology and toxicology↗