Populus (P. tremula X tremuloides-'T89) Lipidbody proteome

Seed lipid bodies (LB), previously viewed as paradigmatic, possess a restricted proteome and serve carbon and energy storage. Albeit present in minute quantities, LBs are widespread in post-germinative tissues, where they display vigorous movement, mediate transient organellar interactions, and shuttle enzymes, and signaling molecules. Storage as well as motility and signaling are relevant in shoot meristems of woody perennials, which ahead of winter produce buds that like seeds establish dormancy, dehydrate, express OLEOSIN genes and accumulate LBs. Unlike seeds, buds do not completely desiccate and LBs retain potential signaling functions. Here, we mapped bud LB production under dormancy-inducing conditions. We found that over an 8-week period LBs enlarged significantly. Concomitantly, three major OLEOSIN family genes were transiently upregulated at the start of bud formation, while in their wake expression of lipid biosynthesis gene DGAT1a/b and lipase gene SDP1a/b increased. In parallel, LDAPa/b, LDAP2a, and LDAP3a/b were upregulated, especially LDAP1b. All LDAPs were localized to LBs. The conclusion that OLEOSINs were replaced by LDAPs was supported by the finding that PUX10a, PUX10b and CDC498A1, involved in OLESOSIN ubiquitination and degradation, were significantly upregulated. Our proteomic analysis identified 723 putative LB proteins. These included LB-anchored Caleosin and LDIP, peripherally associated LDAP1/3 and OBL1, and numerous proteins that reflect storage, transport, organellar interaction, opportunistic cargo and contaminants. There is a significant overlap with proteins identified earlier in plasmodesmal proteomes. Collectively, the data support a model in which LBs are part of a pre-installed mechanism that serves dormancy release, survival through winter and regrowth.