Hot topic: Thermosensing in plants

Plants alter their morphology and cellular homeostasis to promote resilience under a variety of heat regimes. Molecular processes that underlie these responses have been intensively studied and found to encompass diverse mechanisms operating across a broad range of cellular components, timescales and temperatures. This review explores recent progress throughout this landscape with a particular focus on thermosensing in the model plant Arabidopsis. Direct temperature sensors include the photosensors phytochrome B and phototropin, the clock component ELF3 and an RNA switch. In addition, there are heat‐regulated processes mediated by ion channels, lipids and lipid‐modifying enzymes, taking place at the plasma membrane and the chloroplast. In some cases, the mechanism of temperature perception is well understood but in others, this remains an open question. Potential novel thermosensing mechanisms are based on lipid and liquid–liquid phase separation. Finally, future research directions of high temperature perception and signalling pathways are discussed

Identification of novel candidate phosphatidic acid binding proteins involved in the salt stress response of Arabidopsis thaliana roots

Phosphatidic acid (PA) is a lipid second messenger involved in an array of processes occurring during a plant's life cycle. These include development, metabolism and both biotic and abiotic stress responses. PA levels increase in response to salt, but little is known about its function in the earliest responses to salt stress. In this study, we have combined an approach to isolate peripheral membrane proteins of Arabidopsis thaliana roots with lipid-affinity purification, to identify putative proteins that interact with PA and are recruited to the membrane in response to salt stress. Of the 42 putative PA-binding proteins identified by mass spectrometry, a set of eight new candidate PA-binding proteins accumulated at the membrane fraction after seven minutes of salt stress. Among these were clathrin heavy chain (CHC) isoforms, ANTH-domain clathrin assembly proteins, a putative regulator of potassium transport, two ribosomal proteins, glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and a phosphatidylinositol (PI) 4-kinase. PA-binding and salt-induced membrane recruitment of GAPDH and CHC were confirmed by Western blot analysis of cellular fractions. In conclusion, the approach presented here is an effective way to isolate biologically relevant lipid-binding proteins and provides new leads in the study of PA-mediated salt stress responses in root

The salt stress-induced LPA response in Chlamydomonas is produced via PLA2 hydrolysis of DGK-generated phosphatidic acid

The unicellular green alga Chlamydomonas has frequently been used as a eukaryotic model system to study intracellular phospholipid signaling pathways in response to environmental stresses. Earlier, we found that hypersalinity induced a rapid increase in the putative lipid second messenger, phosphatidic acid (PA), which was suggested to be generated via activation of a phospholipase D (PLD) pathway and the combined action of a phospholipase C/diacylglycerol kinase (PLC/DGK) pathway. Lysophosphatidic acid (LPA) was also increased and was suggested to reflect a phospholipase A(2) (PLA(2)) activity based on pharmacological evidence. The question of PA's and LPA's origin is, however, more complicated, especially as both function as precursors in the biosynthesis of phospho- and galactolipids. To address this complexity, a combination of fatty acid-molecular species analysis and in vivo (32)P-radiolabeling was performed. Evidence is provided that LPA is formed from a distinct pool of PA characterized by a high α-linolenic acid (18:3n-3) content. This molecular species was highly enriched in the polyphosphoinositide fraction, which is the substrate for PLC to form diacylglycerol. Together with differential (32)P-radiolabeling studies and earlier PLD-transphosphatidylation and PLA(2)-inhibitor assays, the data were consistent with the hypothesis that the salt-induced LPA response is primarily generated through PLA(2)-mediated hydrolysis of DGK-generated PA and that PLD or de novo synthesis [via endoplasmic reticulum - or plastid-localized routes] is not a major contributor

Diacylglycerol acyltransferase 1 contributes to freezing tolerance

Freezing limits plant growth and crop productivity, and plant species in temperate zones have the capacity to develop freezing tolerance through complex modulation of gene expression affecting various aspects of metabolism and physiology. While many components of freezing tolerance have been identified in model species under controlled laboratory conditions, little is known about the mechanisms that impart freezing tolerance in natural populations of wild species. Here, we performed a quantitative trait locus (QTL) study of acclimated freezing tolerance in seedlings of Boechera stricta, a highly adapted relative of Arabidopsis thaliana native to the Rocky Mountains. A single QTL was identified that contained the gene encoding ACYL-COA:DIACYLGLYCEROL ACYLTRANSFERASE 1 (BstDGAT1), whose expression is highly cold responsive. The primary metabolic enzyme DGAT1 catalyzes the final step in assembly of triacylglycerol (TAG) by acyl transfer from acyl-CoA to diacylglycerol. Freezing tolerant plants showed higher DGAT1 expression during cold acclimation than more sensitive plants and this resulted in increased accumulation of TAG in response to subsequent freezing. Levels of oligogalactolipids which are produced by SFR2 (SENSITIVE TO FREEZING 2), an indispensable element of freezing tolerance in Arabidopsis, were also higher in freezing tolerant plants. Furthermore, overexpression of AtDGAT1 led to increased freezing tolerance. We propose that DGAT1 confers freezing tolerance in plants by supporting SFR2-mediated remodeling of chloroplast membranes