Downregulation of a CYP74 Rubber Particle Protein Increases Natural Rubber Production in \u3ci\u3eParthenium argentatum\u3c/i\u3e

We report functional genomics studies of a CYP74 rubber particle protein from Parthenium argentatum, commonly called guayule. Previously identified as an allene oxide synthase (AOS), this CYP74 constitutes the most abundant protein found in guayule rubber particles. Transgenic guayule lines with AOS gene expression down-regulated by RNAi (AOSi) exhibited strong phenotypes that included agricultural traits conducive to enhancing rubber yield. AOSi lines had higher leaf and stem biomass, thicker stembark tissues, increased stem branching and improved net photosynthetic rate. Importantly, the rubber content was significantly increased in AOSi lines compared to the wild-type (WT), vector control and AOS overexpressing (AOSoe) lines, when grown in controlled environments both in tissue-culture media and in greenhouse/growth chambers. Rubber particles from AOSi plants consistently had less AOS particle-associated protein, and lower activity (for conversion of 13-HPOT to allene oxide). Yet plants with downregulated AOS showed higher rubber transferase enzyme activity. The increase in biomass in AOSi lines was associated with not only increases in the rate of photosynthesis and non-photochemical quenching (NPQ), in the cold, but also in the content of the phytohormone SA, along with a decrease in JA, GAs, and ABA. The increase in biosynthetic activity and rubber content could further result from the negative regulation of AOS expression by high levels of salicylic acid in AOSi lines and when introduced exogenously. It is apparent that AOS in guayule plays a pivotal role in rubber production and plant growth

Development of DArT marker platforms and genetic diversity assessment of the U.S. collection of the new oilseed crop lesquerella and related species.

The advantages of using molecular markers in modern genebanks are well documented. They are commonly used to understand the distribution of genetic diversity in populations and among species which is crucial for efficient management and effective utilization of germplasm collections. We describe the development of two types of DArT molecular marker platforms for the new oilseed crop lesquerella (Physaria spp.), a member of the Brassicaceae family, to characterize a collection in the National Plant Germplasm System (NPGS) with relatively little known in regards to the genetic diversity and traits. The two types of platforms were developed using a subset of the germplasm conserved ex situ consisting of 87 Physaria and 2 Paysonia accessions. The microarray DArT revealed a total of 2,833 polymorphic markers with an average genotype call rate of 98.4% and a scoring reproducibility of 99.7%. On the other hand, the DArTseq platform developed for SNP and DArT markers from short sequence reads showed a total of 27,748 high quality markers. Cluster analysis and principal coordinate analysis indicated that the different accessions were successfully classified by both systems based on species, by geographical source, and breeding status. In the germplasm set analyzed, which represented more than 80% of the P. fendleri collection, we observed that a substantial amount of variation exists in the species collection. These markers will be valuable in germplasm management studies and lesquerella breeding, and augment the microsatellite markers previously developed on the taxa

Plot of Δ<i>K</i> from K = 2 to 7 (a) and the population structure of 75 <i>P. fendleri</i> accessions at <i>K</i> = 4 (b).

<p>Plot of Δ<i>K</i> from K = 2 to 7 (a) and the population structure of 75 <i>P. fendleri</i> accessions at <i>K</i> = 4 (b).</p

Passport information of additional <i>Physaria</i> and <i>Paysonia</i> accessions genotyped using DArTseq.

*<p>exact geographic coordinates of <i>P. pallida</i> are not supplied since they are in the federal and state list of endangered species.</p

Cluster analysis of <i>Physaria</i> and <i>Paysonia</i> accessions based on 2,833 DArT markers.

<p>The labels denote the germplasm collection numbers and origin. Suffixes indicate respective species (PAR: <i>P. argyraea</i>, PAU: <i>P. auriculata</i>, PFE: <i>P. fendleri</i>, PGO: <i>P. gordonii</i>, PGF: <i>P. grandiflora</i>, PGR: <i>P. gracilis</i>, PKN: <i>P.</i> ‘kathryn’, PLI: <i>P. lindheimeri</i>, PPL: <i>P. pallida</i>, PRC: <i>P. recurvata</i>, PRT: <i>P. rectipes</i>, and PTH: <i>P. thamnophila</i>).</p

Passport information of accessions used in <i>Physaria</i> DArT and DArTseq platform development.

*<p>exact geographic coordinates of <i>P. pallida</i> are not supplied since they are in the federal and state list of endangered species.</p

Comparison of population pairwise Fst values using microarray DArT and DArTseq.

*<p>Values in bold are significant at α = 0.05. Values below diagonal are from microarray DArT and those above diagonal are from DArTseq.</p

Distribution of marker PIC values by DArT platform.

<p>Distribution of marker PIC values by DArT platform.</p

Cluster analysis of <i>Physaria</i> and <i>Paysonia</i> accessions based on 27,748 DArTseq markers.

<p>The labels denote the germplasm collection numbers and origin. Suffixes indicate respective species (PAC: <i>P. acutifolia</i>, PAR: <i>P. argyraea</i>, PAU: <i>P. auriculata</i>, PDE: <i>P. densipila</i>, PDF: <i>P. densiflora</i>, PDO: <i>P. douglasii</i>, PFE: <i>P. fendleri</i>, PGO: <i>P. gordonii</i>, PGF: <i>P. grandiflora</i>, PGR: <i>P. gracilis</i>, PIF: <i>P. inflata</i>, PIN: <i>P. intermedia</i>, PKA: <i>P. kaibabensis</i>, PKN: <i>P.</i> ‘kathryn’, PYL: <i>P. lasiocarpa</i>, PLI: <i>P. lindheimeri</i>, PLT: <i>P. lyrata</i>, PLU: <i>P. ludoviciana</i>, PMC: <i>P. mcvaughiana</i>, PMX: <i>P. mexicana</i>, PPF: <i>P. perforata</i>, PPL: <i>P. pallida</i>, PRC: <i>P. recurvata</i>, PRT: <i>P. rectipes</i>, PST: <i>P. stonensis</i>, PTH: <i>P. thamnophila</i> and PVA: <i>P. valida</i>).</p