Biology subjects

Ma, S. A.

Publications and source records attributed to Ma, S. A..

3 recordsLinked to original sources

bioRxiv2024

Resolving an unconventional non-photochemical quenching signature at the light-to-dark transition

Non-photochemical quenching (NPQ) protects photosynthetic organisms via diverse molecular players contributing at varying timescales. However, in the absence of one of the largest contributors to NPQ, energy-dependent quenching (qE), we observe an unusual but universal phenomenon: a transient increase in quenching in the dark following high light exposure. To mechanistically interrogate this light-to-dark (LtD) NPQ phenotype, we performed chlorophyll fluorescence lifetime snapshot measurements across a diverse array of Arabidopsis mutant backgrounds and chemical treatments. We found that the electrochemical gradient across the thylakoid membrane is essential for this phenomenon. Through analysis of higher-order Arabidopsis mutants, we also found that LtD NPQ is independent of the known forms of photoprotective NPQ, as well as the major and minor light-harvesting complexes (LHCII). Our results point to LtD NPQ as a photoinhibition (qI)-related, reaction center quenching with implications for photoprotection in fluctuating light.

plant biology↗

bioRxiv2023

Chlorophyll to Zeaxanthin Energy Transfer in Non-Photochemical Quenching: An Exciton Annihilation-free Transient Absorption Study

Zeaxanthin (Zea) is a key component in the energy-dependent, rapidly reversible, non-photochemical quenching process (qE) that regulates photosynthetic light harvesting. Previous transient absorption (TA) studies suggested that Zea can participate in direct quenching via Chlorophyll (Chl) to Zea energy transfer. However, the contamination of intrinsic exciton-exciton annihilation (EEA) makes the assignment of TA signal ambiguous. In this study, we present EEA-free TA data using Nicotiana benthamiana thylakoid membranes, including wild type and three NPQ mutants (npq1, npq4, and lut2) generated by CRISPR/Cas9 mutagenesis. Results show a strong correlation between excitation energy transfer from excited Chl Qy to Zea S1 and the xanthophyll cycle during qE activation. Notably, a Lut S1 signal is absent in the npq1 thylakoids which lack zeaxanthin. Additionally, the fifth-order response analysis shows a reduction in the exciton diffusion length (LD) from 55 {+/-} 5 nm to 38 {+/-} 3 nm under high light illumination, consistent with the reduced range of exciton motion being a key aspect of plants response to excess light.

plant biology↗

bioRxiv2020

The Sez6 family inhibits complement at the level of the C3 convertase.

The Sez6 family consists of Sez6, Sez6L, and Sez6L2. Its members are expressed throughout the brain and have been shown to influence synapse numbers and dendritic morphology. They are also linked to various neurological and psychiatric disorders. All Sez6 family members contain 2-3 CUB domains and 5 complement control protein (CCP) domains, suggesting that they may be involved in complement regulation. We show that all Sez6 family members inhibit C3 deposition by the classical and alterative pathways with varying degrees of efficacy. For the classical pathway, Sez6 is a strong inhibitor, Sez6L2 is a moderate inhibitor, and Sez6L is a weak inhibitor. Using Sez6L2 as the representative family member, we show that it specifically deactivates C3 convertases by accelerating the decay or dissociation of the C3 convertase components. Sez6L2 also deactivates C3 convertases of the alternative pathway by serving as a cofactor for Factor I to facilitate the cleavage of C3b. However, Sez6L2 has no cofactor activity toward C4b. In summary, the Sez6 family are novel complement regulators that inhibit C3 convertases.

neuroscience↗