No abstract

Lipid droplets play an essential role in the life cycle of plants by housing lipid storage compounds, usually triacylglycerols, in seeds that are mobilized to support post-germinative growth, prior to photosynthetic establishment. Given this critical role in plant growth and development, the majority of research on plant lipid droplets has focused on their function in seed tissues. For instance, purification of lipid droplets from plant oilseeds resulted in the identification and characterization of the oleosins, which are an abundant class of lipid droplet-surface-associated proteins important for stabilizing lipid droplets during seed desiccation 1-3 and possibly serving as sites for recruitment of lipases that facilitate the breakdown of stored triacylglycerols during seedling establishment. 4 It is now appreciated, however, that lipid droplets have numerous functions beyond lipid storage in seeds and that they are present in nearly all plant cell types, many of which do not accumulate appreciable amounts of lipid, such as the cells in leaves, stems, and roots.5 There is also emerging evidence that lipid droplets are highly dynamic organelles involved in a variety of cellular processes and physiological responses, some of which appear to be conserved among eukaryotes. [6][7][8] Nevertheless, the precise functions of lipid droplets in non-seed cell types in plants are currently poorly understood.In an effort to increase our understanding of lipid droplet biogenesis and functions in plants, we recently characterized the proteome of lipid droplets isolated from the mesocarp of avocado (Persea americana).9 This tissue was selected for analysis since it is a rich source of non-seed lipid droplets that lack the abundant oleosins found in oilseed tissues. Briefly, proteins enriched in the isolated avocado mesocarp lipid droplet fraction were identified using a combination of multi-dimensional protein identification technology and peptide mass fingerprinting, using an avocado RNAseqderived "proteome" for query. Two of the most abundant proteins associated with these lipid droplets were highly similar (86%) in sequence to each other and, thus, were annotated as lipid dropletassociated protein 1 (LDAP1) and LDAP2 ( Fig. 1A; Pam_LDAP1 and Pam_LDAP2). We also showed previously that LDAP1 and LDAP2 gene expression during development of avocado mesocarp increased in correlation with oil accumulation.9 Interestingly, transcriptome analysis of various tissues of oil palm (Elaeis guineensis) revealed the presence of three LDAP-like genes, of which one of While lipid droplets have traditionally been considered as inert sites for the storage of triacylglycerols and sterol esters, they are now recognized as dynamic and functionally diverse organelles involved in energy homeostasis, lipid signaling, and stress responses. unlike most other organelles, lipid droplets are delineated by a half-unit membrane whose protein constituents are poorly understood, except in the specialized case of oleosins, which are associated with seed li...

Natural rubber biosynthesis in guayule (Parthenium argentatum Gray) is associated with moderately cold night temperatures. To begin to dissect the molecular events triggered by cold temperatures that govern rubber synthesis induction in guayule, the transcriptome of bark tissue, where rubber is produced, was investigated. A total of 11,748 quality expressed sequence tags (ESTs) were obtained. The vast majority of ESTs encoded proteins that are similar to stress-related proteins, whereas those encoding rubber biosynthesis-related proteins comprised just over one percent of the ESTs. Sequence information derived from the ESTs was used to design primers for quantitative analysis of the expression of genes that encode selected enzymes and proteins with potential impact on rubber biosynthesis in field-grown guayule plants, including 3-hydroxy-3-methylglutaryl-CoA synthase, 3-hydroxy-3-methylglutaryl-CoA reductase, farnesyl pyrophosphate synthase, squalene synthase, small rubber particle protein, allene oxide synthase, and cis-prenyl transferase. Gene expression was studied for field-grown plants during the normal course of seasonal variation in temperature (monthly average maximum 41.7 °C to minimum 0 °C, from November 2005 through March 2007) and rubber transferase enzymatic activity was also evaluated. Levels of gene expression did not correlate with air temperatures nor with rubber transferase activity. Interestingly, a sudden increase in night temperature 10 days before harvest took place in advance of the highest CPT gene expression level.