Location: Bioproducts ResearchTitle: Analysis of cold-acclimated guayule transcriptome Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/10/2012
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: The perennial shrub commonly know as guayule (Partheniun argentatum), native of the Chihuahuan desert, is a rubber producing plant currently being develop as a domestic source of high quality natural rubber essential for the manufacturing of several consumer products for which the use of synthetic rubber is not an option. Rubber synthesis in guayule occurs in the bark parenchyma tissue, mainly during the winter when night temperatures are moderately cold (6-15 'C). The molecular mechanisms triggered by such cold induction of rubber synthesis are unknown, however, are important to understand for the purpose of improving the plant to maximize rubber production yields. To begin to understand the molecular basis of cold-induced rubber production in guayule, we performed a computational analysis of the transcriptome of a 2 year-old cold-acclimated guayule shrub. A cDNA library from bark parenchyma tissue poly(A) mRNA was made using a modified oligo(dT) primer. Double-stranded cDNA fragments >600 bps were introduced into plasmid DNA maintained in ~1.3 x 106 clones of Escherichia coli. 11,748 quality sequences were generated by randomly sequencing clones, of which 9,021 were unique transcripts. Identities of the cDNA library sequences were assigned based on BlastX searches of the non-redundant NCBI database. The most abundant sequences in our collection were related to stress responses (biotic and abiotic). Several other abundant transcripts have also been reported to be highly abundant in Hevea brasiliensis (the rubber tree). In agreement with previous protein analysis of guayule, cold-acclimated rubber-producing tissue was enriched with allene oxide synthase (AOS) transcript (AOS protein is present in high abundance and intimately associated with guayule rubber particles). Interestingly, transcripts encoding other proteins believed to be associated with rubber particles (e.g. cis-prenyl transferase and small rubber particle protein), or the isoprenoid pathway enzymes that make the precursors for rubber biosynthesis (e.g. the mevalonate pathway enzymes and farnesyl pyrophosphate synthase) were not highly abundant. Altogether, transcripts of enzymes relevant to rubber biosynthesis constituted about 1.1% of the unique transcripts population. Our analysis of cold-acclimated guayule transcriptome, in combination with a seasonal gene expression profile of selected rubber synthesis-related genes, suggest that the cold temperatures associated with abundant rubber synthesis in field plants is not controlling rubber synthesis at the gene expression level. This conclusion opens the possibility of a post-transcriptional point of regulation, and/or the critical cold-inducible gene(s) encoding members of the rubber synthesis machinery remain to be identified.