Oil enzyme protects plants from freezing

14 September 2018

Cold temperatures can lay waste to crops. A study investigating how plants in cold climates protect themselves from freezing sheds light on a novel metabolic pathway that helps plants to survive frost. The study was published in Plant Physiology.

Cold acclimation

When plants experience a period of cold (0°C-8°C), they can become more tolerant to freezing. This phenomenon, commonly known as cold acclimation, involves extensive changes in the plant, including accumulation of sugars and antifreeze proteins, as well as adjustments in growth and development. Cold acclimation is essential to plant survival at temperate latitudes and as such a long-studied subject in basic plant physiology. Cell membranes, and their main building blocks, lipids, are important in this process since they are particularly vulnerable cellular structures when freezing occurs. Their integrity is jeopardized by the formation of ice crystals and the loss of liquid water from cells which causes severe dehydration of the plant cells. Little is known, however, about the mechanisms that make plant membranes more resilient under such harsh conditions.

Model of lipid changes in chloroplasts

Figure 1. Model of lipid changes in chloroplasts in response to freezing. The enzymatic activity of Diacylglycerol Acyltransferase 1 (DGAT1) functions in a metabolic pathway to convert chloroplast lipids (MGDG) to membrane-stabilizing sugar-containing lipids (DGDG,TGDG, TeGDG) and oil (triacylglycerol, TAG). This pathway is active at sub-zero temperatures and contributes to plant survival of frost. See Arisz et al. (2018) for further details.

Enhanced survival

A recent publication by researchers from the research group Plant Cell Biology at the UvA Swammerdam Institute for Life Sciences, in collaboration with researchers from Wageningen University, Duke University (Durham, North Carolina, US) and Dupont Pioneer (Johnston, Iowa, US), has shed light on changes in membranes of chloroplasts that help plants to survive frost (Arisz et al. 2018). Surprisingly, an enzyme known for many decades to be responsible for synthesizing seed oil, Diacylglycerol Acyltransferase 1 (DGAT1), was shown to be active in leaves at freezing temperatures, producing oil (triacylglycerol) for increased freezing tolerance. Comprehensive analysis of lipids suggested that in the same process also sugar-containing lipids were formed, which had previously been found to stabilize chloroplast membranes (Figure 1). As a consequence, plants overexpressing the gene for this oil enzyme showed enhanced survival of freezing.

Subalpine meadow habitat

Figure 2. Subalpine meadow habitat (Idaho, alt. 2390 m) where one of the Boechera stricta populations used in this study was collected.

Adult B. stricta

Figure 3. Adult B. stricta, showing long robust flowering stems and leaves at the base forming a rosette.

Importantly, the gene was first identified in a genome-wide screen of Boechera stricta, a relative of the common model species Arabidopsis (Brassicaceae, cabbage family), growing at high altitudes in the Rocky Mountains (Figures 2 and 3). Natural genetic variation in the chromosomal region turned out to be associated with variation in freezing tolerance. Moreover, tolerant B. stricta plants showed higher expression of the gene and higher accumulation of oil. This research uncovers a key role for DGAT1 in freezing tolerance of subalpine plants.

Green Life Sciences

As temperature extremes are expected to occur more frequently in the future, loss of crop productivity due to frost is becoming a major concern. In this light, investigation of plant adaptations to environmental challenges such as freezing has been chosen as research priority area by the Green Life Sciences cluster at UvA's Faculty of Science.

The article’s lead author, Dr Steven Arisz currently works as senior postdoctoral researcher in the lab of Dr Teun Munnik in the Plant Cell Biology group.

Publication details

The article was highlighted and discussed in a Commentary in the August edition of the journal Plant Physiology: 

Research paper (Open Access):

Arisz SA, Heo J-Y, Koevoets I, Zhao T, van Egmond P, Meyer AJ, Zeng W, Niu X, Wang B, Mitchell-Olds T, Schranz ME, Testerink C. (2018) DIACYLGLYCEROL ACYLTRANSFERASE1 contributes to freezing tolerance. Plant Physiology 177: 1410–1424. http://www.plantphysiol.org/content/early/2018/06/18/pp.18.00503?utm_source=TrendMD&utm_medium=cpc&utm_campaign=Plant_Physiol_TrendMD_0

Published by  Faculty of Science