Woolly mutation with Get02 locus overcomes the polygenic nature of trichome-based pest resistance in tomato

Abstract

Type-IV glandular trichomes, which only occur in the juvenile phase of tomato development, produce acylsugars (AS) that broadly protect against arthropod herbivory. Previously, we introgressed the capacity to retain type-IV trichomes in the adult phase from Solanum galapagense into the cv. Micro-Tom (MT). The resulting MT-Get line contained five loci associated with enhancing the density of type-IV trichomes in adult plants. We genetically dissected MT-Get and obtained a sub-line containing only the locus on chromosome 2 (MT- Get02). This genotype displayed about half the density of type-IV trichomes compared to the wild progenitor. However, when we stacked the gain-of-function allele of WOOLLY, which codes for a HD-ZIP IV transcription factor, MT-Get02/Wo exhibited double the number of type-IV trichomes compared to S. galapagense. This discovery corroborates previous reports positioning WOOLLY as a master regulator of trichome development. AS levels in MT-Get02/Wo were comparable to the wild progenitor, although the composition of AS types differed, especially regarding less AS with medium-length acyl chains. Agronomical parameters of MT-Get02/Wo, including yield, were comparable to MT. Pest resistance assays showed enhanced protection against whitefly, caterpillar, and the fungus Septoria lycopersici. However, resistance levels did not reach that of the wild progenitor, suggesting the specificity of particulars AS types in the pest resistance mechanism. Our findings in trichome-mediated resistance advance the development of robust, naturally resistant tomato varieties, harnessing the potential of natural genetic variation. Moreover, by manipulating only two loci, we achieved exceptional results for a highly complex, polygenic trait, such as herbivory resistance in tomato.