Postdoctoral Research Associate Michigan State University
Plants use their remarkable specialized metabolic capacity to interact with the biotic environment, including deterring and attracting insects and microbes. Solanaceae trichome-synthesized acylsugars confer defense against herbivores and offer the possibility of engineering plants with environmentally safe pesticides. The great phenotypic variation of these metabolites – with mono- and di-saccharide cores and acylchains of C2-C12 found across the family – bears the fingerprint of an evolutionary arms race. An alternative hypothesis is that the diversity is simply the result of genetic drift. Deciphering effects of structurally diverse acylsugars faces the challenge of interference of other defense traits (for example, different levels of alkaloids and terpenes in plants). To critically assess the impact of acylsugars on herbivory, we used CRISPR/Cas9 gene editing of domesticated Solanum lycopersicum and Solanum pennellii (LA0716) wild tomato pathway enzymes to modify the amounts and types of metabolites produced. Knockout lines of the first three acylsugar acyltransferase (ASAT) genes in both backgrounds accumulate no detectable acylsugars, without altering plant growth or trichome development. These lines provide a good ‘null mutant’ background to test the efficacy of acylsugars. We generated isogenic lines differing in sucrose- and glucose-based esters in both S. lycopersicum and S. pennellii backgrounds. These plants provide an ideal system for comparing effects of sugar core on anti-herbivory activity. Finally, cultivated tomato slasat4 mutants lacking acetylated acylsucroses permit us to evaluate the impact of acetyl groups in insect protection. Our results suggest that even the performance of the specialist, Manduca sexta, is hindered by presence of acylsugars, while we observe larger protective effects of acylsucroses than acylglucoses. Because they are not transgenic, the CRISPR mutated plants are suitable for investigating the importance of acylsugars in the field. Moreover, these plants serve as a promising molecular engineering platform that allows for investigation of the mechanisms underpinning specialized metabolic evolution.
Coauthors: Rebekah Holtsclaw – University of Missouri;tong Zhang – South China Agricultural University;Abe Koo – University of Missouri