Genetic Architecture of Capitate Glandular Trichome Density in Florets of Domesticated Sunflower (Helianthus annuus L.).

Qing-Ming Gao,Jarrad R Prasifka,Brent S Hulke,Nolan C Kane,Silas Tittes,Cloe S Pogoda,Stephan Reinert

doi:10.3389/fpls.2017.02227

Abstract

Capitate glandular trichomes (CGT), one type of glandular trichomes, are most common in Asteraceae species. CGT can produce various secondary metabolites such as sesquiterpene lactones (STLs) and provide durable resistance to insect pests. In sunflower, CGT-based host resistance is effective to combat the specialist pest, sunflower moth. However, the genetic basis of CGT density is not well understood in sunflower. In this study, we identified two major QTL controlling CGT density in sunflower florets by using a F4 mapping population derived from the cross HA 300 × RHA 464 with a genetic linkage map constructed from genotyping-by-sequencing data and composed of 2121 SNP markers. One major QTL is located on chromosome 5, which explained 11.61% of the observed phenotypic variation, and the second QTL is located on chromosome 6, which explained 14.06% of the observed phenotypic variation. The QTL effects and the association between CGT density and QTL support interval were confirmed in a validation population which included 39 sunflower inbred lines with diverse genetic backgrounds. We also identified two strong candidate genes in the QTL support intervals, and the functions of their orthologs in other plant species suggested their potential roles in regulating capitate glandular trichome density in sunflower. Our results provide valuable information to sunflower breeding community for developing host resistance to sunflower insect pests.

Highlights

Plant trichomes, the hair-like structures on above-ground plant surfaces, are key features governing interaction with the environment, including biotic and abiotic factors
The Capitate glandular trichomes (CGT) numbers per floret were counted for 239 F4 plants, and 179 plants with good genotypic data quality were selected as the final mapping population
179 F4 plants were classified into three groups (Figure 1). Of these 179 F4 plants, 25 plants (13.9%) had high CGT density which is more than 150 CGT per floret, 109 plants (60.9%) had medium CGT density which is 25–150 CGT per floret and 45 plants (25.2%) had low CGT density which is less than 25 CGT per floret

Summary

Introduction

The hair-like structures on above-ground plant surfaces, are key features governing interaction with the environment, including biotic and abiotic factors. Plant trichomes vary greatly in morphology and function, with at least 300 known types of plant trichomes (Wagner, 1991; Spring, 2000; Werker, 2000). Based on their metabolic activity, plant trichomes are classified into two broad groups: glandular trichomes (GTs) and non-glandular trichomes (non-GTs), which co-exist on plant surfaces like leaves, flowers, stems, and bracts (Hare and Elle, 2002; Rautio et al, 2002). A well-studied example of non-GTs is from the model plant Arabidopsis thaliana, which possesses trichomes that are unicellular, unbranched or with two to five branches (Oppenheimer et al, 1991; Larkin, 1994; Szymanski et al, 2000). GTs have been found on ∼30% of all vascular plants, in dicots

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