Synaptotagmins at the endoplasmic reticulum-plasma membrane contact sites maintain diacylglycerol homeostasis during abiotic stress.

Endoplasmic reticulum-plasma membrane contact sites (ER-PM CS) play fundamental roles in all eukaryotic cells. Arabidopsis thaliana mutants lacking the ER-PM protein tether synaptotagmin1 (SYT1) exhibit decreased PM integrity under multiple abiotic stresses, such as freezing, high salt, osmotic stress, and mechanical damage. Here, we show that, together with SYT1, the stress-induced SYT3 is an ER-PM tether that also functions in maintaining PM integrity. The ER-PM CS localization of SYT1 and SYT3 is dependent on PM phosphatidylinositol-4-phosphate and is regulated by abiotic stress. Lipidomic analysis revealed that cold stress increased the accumulation of diacylglycerol at the PM in a syt1/3 double mutant relative to wild-type while the levels of most glycerolipid species remain unchanged. In addition, the SYT1-green fluorescent protein fusion preferentially binds diacylglycerol in vivo with little affinity for polar glycerolipids. Our work uncovers a SYT-dependent mechanism of stress adaptation counteracting the detrimental accumulation of diacylglycerol at the PM produced during episodes of abiotic stress.

The Arabidopsis tetratricopeptide thioredoxin-like gene family is required for osmotic stress tolerance and male sporogenesis.

TETRATRICOPEPTIDE THIOREDOXIN-LIKE (TTL) proteins are characterized by the presence of six tetratricopeptide repeats in conserved positions and a carboxyl-terminal region known as the thioredoxin-like domain with homology to thioredoxins. In Arabidopsis (Arabidopsis thaliana), the TTL gene family is composed by four members, and the founder member, TTL1, is required for osmotic stress tolerance. Analysis of sequenced genomes indicates that TTL genes are specific to land plants. In this study, we report the expression profiles of Arabidopsis TTL genes using data mining and promoter-reporter ß-glucuronidase fusions. Our results show that TTL1, TTL3, and TTL4 display ubiquitous expression in normal growing conditions but differential expression patterns in response to osmotic and NaCl stresses. TTL2 shows a very different expression pattern, being specific to pollen grains. Consistent with the expression data, ttl1, ttl3, and ttl4 mutants show reduced root growth under osmotic stress, and the analysis of double and triple mutants indicates that TTL1, TTL3, and TTL4 have partially overlapping yet specific functions in abiotic stress tolerance while TTL2 is involved in male gametophytic transmission.

What process is glycolytic stoichiometry optimal for?

It has been proposed that the glycolytic stoichiometry of 2 ATP per glucose is the result of an optimization that maximizes the rate of ATP production. However, using a nonequilibrium thermodynamic approach, we show here that glycolysis operates under optimal output power and not at optimal flow of ATP production. Furthermore, it can be proved that the same maximal output power can be achieved with different stoichiometries. However, changes in the glycolytic stoichiometry would dramatically affect the efficiency of all those cellular processes powered by ATP. Our results suggest that the stoichiometric coefficient, as found in most contemporary cells, may be the outcome of an evolutionary process leading to yield an operative quantum energy for the hydrolysis of ATP.

The ATP paradox is the expression of an economizing fuel mechanism.

The strong negative correlation between glycolytic flux and intracellular ATP concentration observed in yeast has long been an intriguing and counterintuitive phenomenon, which has been referred to as the ATP paradox. Herein, using principles of irreversible thermodynamics it was shown that if the ATP-consuming pathways are more sensitive to extracellular glucose than glycolysis, then upon glucose addition glycolysis performance can switch from an efficient working regime to a dissipative regime, and vice versa, depending on glucose availability. The efficient regime represents a good compromise between high output power and low dissipation, whereas the dissipative working regime offers a higher output power although at a high glucose cost. The physiological and evolutionary implications of this switch strategy are discussed.