The coenzyme thiamine diphosphate displays a daily rhythm in the Arabidopsis nucleus

Abstract

In plants, metabolic homeostasis-the driving force of growth and development-is achieved through the dynamic behavior of a network of enzymes, many of which depend on coenzymes for activity. The circadian clock is established to influence coordination of supply and demand of metabolites. Metabolic oscillations independent of the circadian clock, particularly at the subcellular level is unexplored. Here, we reveal a metabolic rhythm of the essential coenzyme thiamine diphosphate (TDP) in the Arabidopsis nucleus. We show there is temporal separation of the clock control of cellular biosynthesis and transport of TDP at the transcriptional level. Taking advantage of the sole reported riboswitch metabolite sensor in plants, we show that TDP oscillates in the nucleus. This oscillation is a function of a light-dark cycle and is independent of circadian clock control. The findings are important to understand plant fitness in terms of metabolite rhythms.

On the nature of thiamine triphosphate in Arabidopsis

“…The final step of diphosphorylation of thiamine to TDP takes place in the cytosol (Ajjawi et al, 2007). Transporters at the organelle membranes serve to import TDP to supply enzymes reliant on it as a coenzyme (Gerdes et al, 2012, Noordally et al, 2020. On the one hand, regulation of supply and demand is buffered at the genetic level in the nucleus by a riboswitch present in the thiamine biosynthesis gene THIC (Rosado-Souza et al, 2019).…”

“…That is, an abundance of free TDP in the nucleus leads to downregulation of THIC transcripts through alternative splicing (Wachter et al, 2007, Bocobza et al, 2007. It has recently been demonstrated by us that at the cellular level (and in contrast to the tissue level), there is a diel rhythm of free TDP in the nucleus, with the peak in TDP levels occurring early in the day (Noordally et al, 2020). The rhythmic diel pattern of TTP, at the tissue level in shoots, matches very closely to that of nuclear free TDP at the cellular level, and because TTP is found in both the plastids and mitochondria as shown in this study, we propose that it may act as a proxy of free TDP levels in these organelles.…”

“…Nonetheless, if it assumed that free TDP is the precursor of TTP, and TTP is a proxy for organellar levels of free TDP, then, as a corollary, interconversion of organellar TDP and TTP may serve to regulate TDP levels in the organelle powerhouses on a daily basis. As TDP levels are maximal during the day (as evidenced indirectly from the performance of the riboswitch) (Noordally et al, 2020), conversion to TTP may dissipate excess levels in the plastids and mitochondria. In this context, it is relevant to consider that enzyme targets of TTP have been identified in mammalian brain cell extracts (Mkrtchyan et al, 2015).…”

“…at the end of the dark period ( Figure 5A). It should be noted that we have recently demonstrated that none of the other well-characterized B 1 vitamers (TDP, TMP, or thiamine) display an oscillation at the tissue level in plants (Noordally et al, 2020). As diurnal oscillations are frequently regulated by the genetically encoded circadian clock, we next examined if the circadian clock anticipated the oscillations.…”

The importance of thiamine (vitamin B1) in plant health: From crop yield to biofortification

“…Transporters specific for TDP at the mitochondrial membrane are known and are annotated as thiamine pyrophosphate carriers (TPCs) (39). Arabidopsis has two members (TPC1 and TPC2), which have recently been shown to be vital for plant survival (40) (Fig. 3).…”