OeFAD8, OeLIP and OeOSM expression and activity in cold-acclimation of Olea europaea, a perennial dicot without winter-dormancy

Abstract

Main conclusionCold-acclimation genes in woody dicots without winter-dormancy, e.g., olive-tree, need investigation. Positive relationships betweenOeFAD8, OeOSM, andOeLIP19and olive-tree cold-acclimation exist, and couple with increased lipid unsaturation and cutinisation.Olive-tree is a woody species with no winter-dormancy and low frost-tolerance. However, cold-tolerant genotypes were empirically selected, highlighting that cold-acclimation might be acquired. Proteins needed for olive-tree cold-acclimation are unknown, even if roles for osmotin (OeOSM) as leaf cryoprotectant, and seed lipid-transfer protein for endosperm cutinisation under cold, were demonstrated. In other species, FAD8, coding a desaturase producing α-linolenic acid, is activated by temperature-lowering, concomitantly with bZIP-LIP19 genes. The research was focussed on finding OeLIP19 gene(s) in olive-tree genome, and analyze it/their expression, and that of OeFAD8 and OeOSM, in drupes and leaves under different cold-conditions/developmental stages/genotypes, in comparison with changes in unsaturated lipids and cell wall cutinisation. Cold-induced cytosolic calcium transients always occurred in leaves/drupes of some genotypes, e.g., Moraiolo, but ceased in others, e.g., Canino, at specific drupe stages/cold-treatments, suggesting cold-acclimation acquisition only in the latter genotypes. Canino and Moraiolo were selected for further analyses. Cold-acclimation in Canino was confirmed by an electrolyte leakage from leaf/drupe membranes highly reduced in comparison with Moraiolo. Strong increases in fruit-epicarp/leaf-epidermis cutinisation characterized cold-acclimated Canino, and positively coupled with OeOSM expression, and immunolocalization of the coded protein. OeFAD8 expression increased with cold-acclimation, as the production of α-linolenic acid, and related compounds. An OeLIP19 gene was isolated. Its levels changed with a trend similar to OeFAD8. All together, results sustain a positive relationship between OeFAD8, OeOSM and OeLIP19 expression in olive-tree cold-acclimation. The parallel changes in unsaturated lipids and cutinisation concur to suggest orchestrated roles of the coded proteins in the process.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-016-2490-x) contains supplementary material, which is available to authorized users.

Unsaturated Lipids Change in Olive Tree Drupe and Seed during Fruit Development and in Response to Cold-Stress and Acclimation

“…The cold sensitivity also decreases, but in a genotype-dependent manner. Around WAF19, cold acclimation is acquired by the drupes of the genotypes capable of cold acclimation in the leaves, e.g., Canino, whereas cold sensitivity persists in the drupes of genotypes maintaining cold sensitivity, e.g., Moraiolo [7]. …”

“…The differences in drupe cold-responsiveness remain among the genotypes, however, OB size is constant [5,7]. …”

“…The quality of olive oil is directly related to the physiological state of the drupe from which is extracted [9], and the cold response of the drupe is important [5,7]. Phenolic compounds, lipids, tocopherols, and pigments, such as carotenoids and chlorophylls, contribute to determine the oil quality, and its organoleptic properties.…”

“…Interest in olive tree cultivation is progressively extending to countries outside the Mediterranean Basin, e.g., Argentina, Western Africa, Australia, Azerbaijan, China, and Japan [3,4], where the plants have to survive to colder winters [5]. However, many genotypes show low frost-tolerance [6,7] and become less, or non-, productive under unfavourable environmental conditions. Olive tree is a cultigen complex [8], composed of about 2600 genotypes in the Mediterranean regions.…”

“…Moraiolo. In a series of studies with these genotypes, the acquisition or non-acquisition of cold-acclimation was revealed by monitoring the absence and presence, respectively, of cold-induced transient changes of cytosolic calcium levels in protoplasts from both leaves and drupes [5,6,7,12]. …”