Davis, J. A. | Search bioRxiv

bioRxiv2021

Increasing seed thiamin content impacts stored carbon partitioning and subsequent seedling stress tolerance

Thiamin and thiamin pyrophosphate (TPP) are essential components for the function of enzymes involved in the metabolism of carbohydrates and amino acids in living organisms. In addition to its role as a cofactor, thiamin plays a key role in resistance against biotic and abiotic stresses in plants. Most of the studies used exogenous thiamin to enhance stress tolerance in plants. In this study, we achieved this objective by genetically engineering Arabidopsis thaliana and Camelina sativa for the seed-specific co-overexpression of the Arabidopsis thiamin biosynthetic genes Thi4, ThiC, and ThiE. Elevated thiamin content in the seeds of transgenic plants was accompanied by the enhanced expression levels of transcripts encoding thiamin cofactor-dependent enzymes. Furthermore, seed germination and root growth in thiamin over-producing lines were more tolerant to oxidative stress caused by salt and paraquat treatments. The transgenic seeds also accumulated more oil (up to16.4% in Arabidopsis and17.9% in C. sativa) and carbohydrate but less protein than the control seeds. The same results were also observed in TPP over-producing Arabidopsis plants generated by the seed-specific overexpression of TPK1. Together, our findings suggest that thiamin and TPP over-production in transgenic lines confer a boosted abiotic stress tolerance and alter the seed carbon partitioning as well.

bioengineering↗

bioRxiv2021

Impaired clock gene expression and abnormal diurnal regulation of hippocampal inhibitory transmission and spatial memory in a mouse model of Alzheimers disease

Patients with Alzheimers disease (AD) often have fragmentation of sleep/wake cycles and disrupted 24-h (circadian) activity. Despite this, little work has investigated the potential underlying day/night disruptions in cognition and neuronal physiology in the hippocampus. The molecular clock, an intrinsic transcription-translation feedback loop that regulates circadian behavior, may also regulate hippocampal neurophysiological activity. We hypothesized that disrupted diurnal variation in clock gene expression in the hippocampus corresponds with loss of normal day/night differences in membrane excitability, synaptic physiology, and cognition. We previously reported that the Tg-SwDI mouse model of AD has disrupted circadian locomotor rhythms and neurophysiological output of the suprachiasmatic nucleus (the primary circadian clock). Here, we report that Tg-SwDI mice failed to show day-night differences in a spatial working memory task, unlike wild-type controls that exhibited enhanced spatial working memory at night. Moreover, Tg-SwDI mice had lower levels of Per2, one of the core components of the molecular clock, at both mRNA and protein levels when compared to age-matched controls. Interestingly, we discovered neurophysiological impairments in area CA1 of the Tg-SwDI hippocampus. In controls, spontaneous inhibitory post-synaptic currents (sIPSCs) in pyramidal cells showed greater amplitude and lower inter-event interval during the day than the night. However, the normal day/night differences in sIPSCs were absent (amplitude) or reversed (inter-event interval) in pyramidal cells from Tg-SwDI mice. In control mice, current injection into CA1 pyramidal cells produced more firing during the night than during the day, but no day/night difference in excitability was observed in Tg-SwDI mice. The normal day/night difference in excitability in controls was blocked by GABA receptor inhibition. Together, these results demonstrate that the normal diurnal regulation of inhibitory transmission in the hippocampus is diminished in a mouse model of AD, leading to decreased daytime inhibition onto hippocampal CA1 pyramidal cells. Uncovering disrupted day/night differences in circadian gene regulation, hippocampal physiology, and memory in AD mouse models may provide insight into possible chronotherapeutic strategies to ameliorate Alzheimers disease symptoms or delay pathological onset.

neuroscience↗