novel role for oleosins in freezing tolerance of oilseeds in Arabidopsis thaliana

• Published in: The Plant journal : for cell and molecular biology Vol. 55; no. 5; pp. 798 - 809
• Main Authors: Shimada, Takashi L, Shimada, Tomoo, Takahashi, Hideyuki, Fukao, Yoichiro, Hara-Nishimura, Ikuko
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-09-2008; Blackwell Publishing Ltd; Blackwell Science
• Subjects: Adaptation to environment and cultivation conditions; Agronomy. Soil science and plant productions; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - ultrastructure; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Biological and medical sciences; Botany; DNA, Bacterial - genetics; DNA, Plant - genetics; Freezing; Fundamental and applied biological sciences. Psychology; Genes, Plant; Genetics; Genetics and breeding of economic plants; Germination - genetics; lipid bodies; Microscopy, Electron, Transmission; Mutagenesis, Insertional; Mutation; oil bodies; Oils & fats; oilseeds; oleosins; Plant Oils - metabolism; Seeds; Seeds - genetics; Seeds - metabolism; Seeds - ultrastructure; Varietal selection. Specialized plant breeding, plant breeding aims; Seeds; Germination; Mortality; Imbibition; Tolerance; oleosins; Arabidopsis thaliana; oilseeds; freezing; Cruciferae; Dicotyledones; Angiospermae; oil bodies; Spermatophyta; Mutation; Low temperature
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313x.2008.03553.x

Oil bodies in seeds of higher plants are surrounded with oleosins. Here we demonstrate a novel role for oleosins in protecting oilseeds against freeze/thaw-induced damage of their cells. We detected four oleosins in oil bodies isolated from seeds of Arabidopsis thaliana, and designated them OLE1, OLE2, OLE3 and OLE4 in decreasing order of abundance in the seeds. For reverse genetics, we isolated oleosin-deficient mutants (ole1, ole2, ole3 and ole4) and generated three double mutants (ole1 ole2, ole1 ole3 and ole2 ole3). Electron microscopy showed an inverse relationship between oil body sizes and total oleosin levels. The double mutant ole1 ole2, which had the lowest levels of oleosins, had irregular enlarged oil-containing structures throughout the seed cells. Germination rates were positively associated with oleosin levels, suggesting that defects in germination are related to the expansion of oil bodies due to oleosin deficiency. We found that freezing followed by imbibition at 4°C abolished seed germination of single mutants (ole1, ole2 and ole3), which germinated normally without freezing treatment. The treatment accelerated the fusion of oil bodies and the abnormal-positioning and deformation of nuclei in ole1 seeds, which caused seed mortality. In contrast, ole1 seeds that had undergone freezing treatment germinated normally when incubated at 22°C instead of 4°C, because degradation of oils abolished the acceleration of fusion of oil bodies during imbibition. Taken together, our findings suggest that oleosins increase the viability of over-wintering oilseeds by preventing abnormal fusion of oil bodies during imbibition in the spring.