Abstract
In an alternative pathway to acyl-CoA: diacylglycerol acyltransferase (DGAT)-mediated triacylglycerol (TAG) synthesis from diacylglycerol, phospholipid:diacylglycerol acyltransferase (PDAT) utilizes not acyl-CoA but an acyl group from sn-2 position of a phospholipid, to form TAG. The enzyme’s activity in vitro matches DGAT’s in a number of plant species, however its main function in plants (especially in vegetative tissue) is debatable. In the presented study, we cultivated PDAT1-overexpressing, pdat1 knockout and wild-type lines of Arabidopsis thaliana through their whole lifecycle. PDAT1 overexpression prolonged Arabidopsis lifespan in comparison to wild-type plants, whereas knocking out pdat1 accelerated the plant’s senescence. After subjecting the 3-week old seedlings of the studied lines (grown in vitro) to 2-h heat stress (40°C) and then growing them for one more week in standard conditions, the difference in weight between wild-type and PDAT1-overexpressing lines increased in comparison to the difference between plants grown only in optimal conditions. In another experiment all lines exposed to 2-week cold stress experienced loss of pigment, except for PDAT1-overexpressing lines, which green rosettes additionally weighed 4 times more than wild-type. Our results indicate that plants depleted of PDAT1 are more susceptible to cold exposure, while PDAT1 overexpression grants plants a certain heat and cold resilience. Since it was shown, that lysophospholipids may be intertwined with stress response, we decided to also conduct in vitro assays of acyl-CoA:lysophosphatidylcholine acyltransferase (LPCAT) and acylCoA:lysophosphatidylethanolamine acyltransferase (LPEAT) activity in microsomal fractions from the PDAT1-overexpressing Arabidopsis lines in standard conditions. The results show significant increase in LPEAT and LPCAT activity in comparison to wild-type plants. PDAT1-overexpressing lines’ rosettes also present twice as high expression of LPCAT2 in comparison to control. The presented study shows how much heightened expression of PDAT1 augments plant condition after stress and extends its lifespan.
Highlights
Triacylglycerols (TAG) are a plant’s way of storing high-dense energy, being twice as energy-efficient as equivalent mass of carbohydrates or protein (Xu and Shanklin, 2016)
We began our journey into investigating AtPDAT1 by studying phenotypic differences between selected pdat1 knockout mutants and PDAT1-overexpressing lines, as well as wild-type Arabidopsis thaliana
Wild-type and mutant lines went through the main milestones in flower development at similar points in time, from first appearance of flower buds, through first flower opening to cessation of flowering, understood as all flowers on a single plant becoming siliques
Summary
Triacylglycerols (TAG) are a plant’s way of storing high-dense energy, being twice as energy-efficient as equivalent mass of carbohydrates or protein (Xu and Shanklin, 2016). In the year 2000 an enzyme was discovered, which was able to form TAG not by utilizing acylCoA, but by taking an acyl group from a phospholipid (most of the time phosphatidylcholine or phosphatidylethanolamine) and transferring it to the sn-3 position of DAG. This enzyme has been known ever since as phospholipid:diacylglycerol acyltransferase (PDAT; Banas et al, 2000; Dahlqvist et al, 2000)
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