Biochemical and genetic characterization of rubber production in prickly lettuce (Lactuca serriola L.)

Natural rubber (cis-1,4-polyisoprene) is one of the most important plant derived bio-polymers used in the manufacture of thousands of products. Plant originated rubber is unique in that the physical properties such as tensile strength, heat and impact resistance have yet to be reproduced by synthetic polyisoprene. While many plants are able to make rubber polymers, few can synthesize high molecular weight molecules. Prickly lettuce ( Lactuca serriola L.), a common weed, is one of the few. The following studies were conducted to assess the diversity, genetics, the chemical and physical properties as well as the microscopic elements related to prickly lettuce rubber production. Rubber from a collection of eastern Washington prickly lettuce biotypes revealed variation in rubber content and quality, although all biotypes synthesized high molecular weight rubber. Two distinct biotypes were crossed and selfed to generate an F2 segregating population. Plant phenotypes and genetic segregation of markers (EST-SSRs) were collected to discover marker-trait associations or quantitative trait loci (QTL). Four main QTL were discovered corresponding to the following traits; rubber molecular weight, leaf perimeter and leaf lobing, stem counts and growth habit, and herbivory. A single marker association was observed with the trait rubber polymer dispersity. Rubber extraction methods were evaluated and found that chemical extraction of dried, ground whole plant material yielded little rubber of low quality. Direct rubber extraction from tapped latex was the best extraction method. Rubber polymers were confirmed as cis-1,4-polyisoprene by nuclear magnetic resonance spectroscopy with little to no trans -polyisoprene detected. Physical property analysis showed that prickly lettuce rubber has properties equal to or better than rubber derived from Brazilian rubber tree. Prickly lettuce is a potential source of natural rubber having the desired physical properties for end-use production. Production feasibility will rely on rubber trait selection and extraction optimization to increase yield. Prickly lettuce can also serve as a model species to understand rubber biosynthesis as it is highly amenable to genetic and biochemical experimentation. These studies have extended the foundation of understanding towards the biosynthesis and utilization of rubber in prickly lettuce.