Cycloartane- and Lanostane-Type Triterpenoids from the Resin of Parthenium argentatum AZ-2, a Byproduct of Guayule Rubber Production.

A total of 12 new cycloartane- and lanostane-type triterpenoids including 16-deoxyargentatin A (1), 16-deoxyisoargentatin A (2), 7-oxoisoargentatin A (3), 24-epi-argentatin H (4), 24-O-p-anisoylargentatin C (5), 24-O-trans-cinnamoylargentatin C (6), 16-dehydroargentatin C (7), 16,17(20)-didehydroargentatin C (8), isoargentatin C (9), isoargentatin H (10), 3-epi-quisquagenin (11), and isoquisquagenin (12) together with 10 known triterpenoids (13-22) were isolated from the resin of Parthenium argentatum AZ-2 obtained as a byproduct of Bridgestone guayule rubber production. The structures of new triterpenoids 1-12 and argentatin H (13), which has previously been characterized as its diacetate (23), were elucidated by extensive analysis of their spectroscopic data and chemical conversions, and the known compounds 14-22 were identified by comparison of their spectroscopic data with those reported. Of these, 13, 14, and 18 exhibited weak cytotoxic activity for several cancer cell lines.

Downregulation of a CYP74 Rubber Particle Protein Increases Natural Rubber Production in Parthenium argentatum.

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.

Phenotypic changes and DNA methylation status in cryopreserved seeds of rye (Secale cereale L.).

Conserving genetic diversity is a major priority of the National Laboratory for Genetic Resources Preservation (NLGRP), operated by the U.S. Department of Agriculture, Agricultural Research Service. There are two long-term preservation methods employed in the NLGRP: storage in a -18 °C freezer (conventional storage) and storage in liquid nitrogen vapor phase at -135 to -180 °C (cryopreservation). To test the phenotypic and epigenetic effects of long-term cryopreservation of orthodox seeds, we evaluated 40 cereal rye accessions (20 spring habit and 20 winter habit) stored for 25 years under both conventional storage and cryogenic conditions. In laboratory evaluations of winter habit rye, seeds from cryopreserved samples had significantly higher normal germination percentage (P < 0.05) and lower abnormal germination percentage (P < 0.05) than those stored under conventional conditions. Cryopreserved spring habit rye also had higher normal germination percentage (P < 0.01) than conventionally stored samples. In addition, winter rye seedlings from cryopreserved seeds had longer roots and smaller root diameter (P < 0.05) than seedlings from conventionally stored seeds. In field evaluations conducted in Fort Collins, Colorado in 2014-15, spikes of plants grown from conventionally stored seeds of the winter accessions were slightly longer than those from cryopreserved seeds (P = 0.045). To detect DNA methylation changes, a methylation-sensitive amplified fragment length polymorphism (metAFLP) technique was applied to two accessions. After false discovery rate adjustment, no differences in methylation were detected between storage treatments on an individual locus basis. Our study indicated that cryopreservation slowed seed deterioration as evidenced by higher germination rates compared to conventional storage, had only minimal effects on other phenotypic traits, and had no significant effects on DNA methylation status.

Root traits contributing to plant productivity under drought.

Geneticists and breeders are positioned to breed plants with root traits that improve productivity under drought. However, a better understanding of root functional traits and how traits are related to whole plant strategies to increase crop productivity under different drought conditions is needed. Root traits associated with maintaining plant productivity under drought include small fine root diameters, long specific root length, and considerable root length density, especially at depths in soil with available water. In environments with late season water deficits, small xylem diameters in targeted seminal roots save soil water deep in the soil profile for use during crop maturation and result in improved yields. Capacity for deep root growth and large xylem diameters in deep roots may also improve root acquisition of water when ample water at depth is available. Xylem pit anatomy that makes xylem less "leaky" and prone to cavitation warrants further exploration holding promise that such traits may improve plant productivity in water-limited environments without negatively impacting yield under adequate water conditions. Rapid resumption of root growth following soil rewetting may improve plant productivity under episodic drought. Genetic control of many of these traits through breeding appears feasible. Several recent reviews have covered methods for screening root traits but an appreciation for the complexity of root systems (e.g., functional differences between fine and coarse roots) needs to be paired with these methods to successfully identify relevant traits for crop improvement. Screening of root traits at early stages in plant development can proxy traits at mature stages but verification is needed on a case by case basis that traits are linked to increased crop productivity under drought. Examples in lesquerella (Physaria) and rice (Oryza) show approaches to phenotyping of root traits and current understanding of root trait genetics for breeding.

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.

Impact of Lygus spp. (Hemiptera: Miridae) on damage, yield and quality of lesquerella (Physaria fendleri), a potential new oil-seed crop.

Lesquerella, Physaria fendleri (A. Gray) S. Watson, is a mustard native to the western United States and is currently being developed as a commercial source of valuable hydroxy fatty acids that can be used in a number of industrial applications, including biolubricants, biofuel additives, motor oils, resins, waxes, nylons, plastics, corrosion inhibitors, cosmetics, and coatings. The plant is cultivated as a winter-spring annual and in the desert southwest it harbors large populations of arthropods, several of which could be significant pests once production expands. Lygus spp. (Hemiptera: Miridae) are common in lesquerella and are known pests of a number of agronomic and horticultural crops where they feed primarily on reproductive tissues. A 4-yr replicated plot study was undertaken to evaluate the probable impact of Lygus spp. on production of this potential new crop. Plant damage and subsequent seed yield and quality were examined relative to variable and representative densities of Lygus spp. (0.3-4.9 insects per sweep net) resulting from variable frequency and timing of insecticide applications. Increasing damage to various fruiting structures (flowers [0.9-13.9%], buds [1.2-7.1%], and seed pods [19.4-42.5%]) was significantly associated with increasing pest abundance, particularly the abundance of nymphs, in all years. This damage, however, did not consistently translate into reductions in seed yield (481-1,336 kg/ha), individual seed weight (0.5-0.7 g per 1,000 seed), or seed oil content (21.8-30.4%), and pest abundance generally explained relatively little of the variation in crop yield and quality. Negative effects on yield were not sensitive to the timing of pest damage (early versus late season) but were more pronounced during years when potential yields were lower due to weed competition and other agronomic factors. Results suggest that if the crop is established and managed in a more optimal fashion, Lygus spp. may not significantly limit yield. Nonetheless, additional work will be needed once more uniform cultivars become available and yield effects can be more precisely measured. Densities of Lygus spp. in unsprayed lesquerella are on par with those in other known agroecosystem level sources of this pest (e.g., forage and seed alfalfa, Medicago sativa L.). Thus, lesquerella production may introduce new challenges to pest management in crops such as cotton.

Evaluation of new Lesquerella and Physaria (Brassicaceae) oilseed germplasm.

The seed oil of Lesquerella and the closely related genus Physaria (Brassicaceae) is rich in hydroxy fatty acids (HFAs). HFAs and their derivatives are used to produce a variety of industrial products including lubricants, nylon-11, plastics, drying agents, protective coatings, surfactants, cosmetics, and pharmaceuticals. Lesquerella fendleri is being developed as a new crop for arid regions of the southwestern United States as an alternative source of HFAs. Between 1995 and 2001, 66 accessions from 28 species of Lesquerella were collected in the United States, 33 accessions from four species were collected in Mexico, and 41 accessions from 15 species of Physaria were collected from the southwestern United States. Mean seed mass ranged from 0.54 to 2.30 mg for Lesquerella compared to 1.70 to 5.80 mg for Physaria. Seed oil content ranged from a high of 32.2% in Lesquerella to a high of 35.4% in Physaria. The fatty acid profile of all species of Physaria and most of the lesquerolic-acid-rich species of Lesquerella contained from 30 to 55% lesquerolic acid, although several species contained >60%. These collections of wild germplasm provide a diverse gene pool that should enhance our breeding program in developing a domestic source of HFAs.