Leaf lipidome and transcriptome profiling of Portulaca oleracea: characterization of lysophosphatidylcholine acyltransferase.

Poly-unsaturated fatty acids (PUFAs) are gaining importance due to their innumerable health benefits, and hence, understanding
their biosynthesis in plants has attained prominence in recent years. The most common source of PUFAs is of marine
origin. Although reports have identified Portulaca oleracea (purslane) as a leaf source of omega-3 fatty acids in the form
of alpha-linolenic acid (ALA), the mechanism of ALA accumulation and its distribution into various lipids has not been
elucidated. Here, we present the lipid profiles of leaves and seeds of several accessions of P. oleracea. Among the nineteen
distinct accessions, the RR04 accession has the highest amount of ALA and is primarily associated with galactolipids.
In addition, we report the transcriptome of RR04, and we have mapped the potential genes involved in lipid metabolism.
Phosphatidylcholine (PC) is the major site of acyl editing, which is catalyzed by lysophosphatidylcholine acyltransferase
(LPCAT), an integral membrane protein that plays a major role in supplying oleate to the PC pool for further unsaturation.
Our investigations using mass spectrometric analysis of leaf microsomal fractions identified LPCAT as part of a membrane
protein complex. Both native and recombinant LPCAT showed strong acyltransferase activity with various acyl-CoA substrates.
Altogether, the results suggest that ALA-rich glycerolipid biosynthetic machinery is highly active in nutritionally
important Portulaca leaves. Furthermore, lipidome, transcriptome, and mass spectrometric analyses of RR04 provide novel
information for exploring Portulaca as a potential resource and a model system for studying leaf lipid metabolism.