Zhonghua Wang1, Yong Wang1, Reinhard Jetter2
1 College of Agronomy, Northwest A&F University
2 Department of Botany, University of British Columbia

The cuticle of plants is the first protective barrier against the biotic and abiotic stresses from the environment. The components of cuticle include cutin and cuticular waxes which are diversified in different species. Cuticular waxes are known to play a critical role in limiting transpirational water loss across plant surfaces. Comparing to leaves the astomatous tomato fruit is an ideal model system that permits the functional characterization of intact cuticular membranes and therefore allows direct correlation of their permeability for water with their qualitative and quantitative waxes composition.
Composition of tomato cuticular waxes can be categorized as two group compounds. One derived from very long chain fatty acid, mainly consisted of alkanes, alkanols and alkanoic acids. Reduction of the intracuticular aliphatics in the lecer6 mutant to approximately 50% caused a 4‐fold increase in water permeability. Hence, the main portion of the transpiration barrier is located in the intracuticular wax layer, largely determined by the aliphatic constituents. LeCER6 encodes a very-long-chain fatty acid elongase β-ketoacyl-CoA synthase, which involved in the biosynthesis of aliphatic compounds. Another group compounds derived from isoprene include pentacyclic triterpenoids, sterol derivatives. Triterpenoids, which are a group of natural products with important biological functions and medicinal properties, such as anti-microbial activities and anti-inflammatory, were the major components of cuticular waxes in the early development stage in tomato.  More than 10 compounds of triterpenoid have been identified from tomato waxes and the pattern of the triterpenoids remained constant over the ripening stages and different cultivars. To understand the biosynthesis of these triterpenoids, two genes were isolated from tomato fruits and functionally characterized in yeast. Based on the products profiles of these two genes, SlTTS 1 encodes a β-amyrin synthase which produced single product β-amyrin; SlTTS 2 encodes a multifunctional triterpene synthase. The compounds gas chromatography profiles of these two genes displayed a good match with the triterpenoids peak pattern in cuticular waxes, this indicated that all triterpenoids detected in the fruit waxes can be synthesized by the enzymes encoded by SlTTS 1 and SlTTS 2.
Drought resistant plants K. daigremontiana and K. mamorata are two species of Kalanchoe, which is a genus of about 125 species of succulent flowering plants in the family Crassulaceae These plants are cultivated as ornamental houseplants and garden plants. They are popular because of their ease of propagation, low water requirements, and wide variety of flower colors. As an adaptation to arid conditions CAM photosynthesis (Crassulacean Acid Metabolism) is their carbon fixation pathway. The stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO2).The waxes on the plant surface are critical for their water saving and survive. To understand the mechanisms of their water saving strategies, leaf waxes compositions were analyzed qualitatively and quantitatively by using GC-FID/MS. Triterpenoids and alkanes are the major compounds of their waxes. We cloned 5 genes encoding oxidosqualene cyclase which involved in the biosynthesis of wax triterpenoids.