Pathways for Synthesis, and Possibilities for Genetic Modification of Sugar Ester Acyl Groups Produced by Trichomes of Solanaceous Species

Glandular trichomes of many plant species synthesize and secrete a variety of phytochemicals that play an important protective role against pathogens and pests. Acyl sugars, in particular, are powerful natural insecticides. We demonstrated the existence of the α-ketoacid elongation (αKAE) pathway, an alternative to the fatty acid synthase (FAS) pathway, for the extension of carbon chains of acyl groups in sugar esters (SE). The α-KAE pathway utilizes one carbon elongation per cycle in contrast to two carbons per cycle in FAS, and it was found to function in a variety of tobaccos and petunia. FAS-mediated elongation was confirmed to participate in the synthesis of SE acyl groups in Solanum pennellii and Datura metel, and also in the synthesis of odd-carbon-length acids of epicuticular waxes from in tobacco and Brassica oleraceae. We attempted to knock down (RNAi-mediated) the central for the α-KAE pathway condensing enzyme isopropyl malate synthase (IPMS) using two IPMS-related genes from S. pennellii. The RNAi constructs were introduced via Agrobacterium-mediated transformation of leaf discs of N. tabacum T.I. 1068, and the resulting plants displayed significant changes in 2-methylbutyric and 3-methylvaleric groups produced by glandular trichomes.