Imaging heterogeneity of membrane and storage lipids in transgenic Camelina sativa seeds with altered fatty acid profiles

Abstract

SUMMARYEngineering compositional changes in oilseeds is typically accomplished by introducing new enzymatic step (s) and/or by blocking or enhancing an existing enzymatic step(s) in a seed-specific manner. However, in practice, the amounts of lipid species that accumulate in seeds are often different from what one would predict from enzyme expression levels, and these incongruences may be rooted in an incomplete understanding of the regulation of seed lipid metabolism at the cellular/tissue level. Here we show by mass spectrometry imaging approaches that triacylglycerols and their phospholipid precursors are distributed differently within cotyledons and the hypocotyl/radicle axis in embryos of the oilseed crop Camelina sativa, indicating tissue-specific heterogeneity in triacylglycerol metabolism. Phosphatidylcholines and triacylglycerols enriched in linoleic acid (C18:2) were preferentially localized to the axis tissues, whereas lipid classes enriched in gadoleic acid (C20:1) were preferentially localized to the cotyledons. Manipulation of seed lipid compositions by heterologous over-expression of an acyl-acyl carrier protein thioesterase, or by suppression of fatty acid desaturases and elongases, resulted in new overall seed storage lipid compositions with altered patterns of distribution of phospholipid and triacylglycerol in transgenic embryos. Our results reveal previously unknown differences in acyl lipid distribution in Camelina embryos, and suggest that this spatial heterogeneity may or may not be able to be changed effectively in transgenic seeds depending upon the targeted enzyme(s)/pathway(s). Further, these studies point to the importance of resolving the location of metabolites in addition to their quantities within plant tissues.

Tracking the metabolic pulse of plant lipid production with isotopic labeling and flux analyses: Past, present and future

“…The metabolite heterogeneity including lipid compositions at the cellular level examined through MRI [288,289] and imaging mass spec [290][291][292][293] is visually striking [see figures and further description in [294]] and reminds us that plants operate at a systems level ( Fig. 1) with individual cells predisposed to differing metabolic objectives.…”

Spatial Mapping and Profiling of Metabolite Distributions during Germination

“…Such nonuniform distribution has been observed previously in cotton (Gossypium hirsutum; Horn et al, 2012) and Camelina spp. seeds (Horn et al, 2013); thus, this is not unique to maize but, apparently, is a more general phenomenon. However, the specifics of the distribution are unique for each species, likely owing to the different anatomy and biological properties of these seeds.…”

New features of triacylglycerol biosynthetic pathways of peanut seeds in early developmental stages

“…In addition to seeds, TAG synthesis can also be accumulated in the flower petals, anthers, pollen grains, and leaves of a number of plant species (Kaup et al 2002;Kim et al 2002). However, the pathways of TAG synthesis appear to differ among plant species (Voelker and Kinney 2001;Troncoso-Ponce et al 2011) and plant tissues (Horn et al 2013), and their differences need to be further identified.…”