Glucosinolates are produced in trichomes of Arabidopsis thaliana

Abstract

Glucosinolates (GS) are important plant secondary metabolites in plant resistance to herbivores, bacteria, and fungi, which have been shown to be accumulating in different organs and tissue types at varying concentrations. There are more than 200 GS species found in order Brassicales and presence of these compounds is well documented on organ-specific but not on cell-specific level. We used UPLC/ESI-QTOF-MS to measure the presence of GS and qRT-PCR to analyse the expression of GS biosynthetic and regulatory genes in isolated Arabidopsis thaliana trichomes. Trichomes of Arabidopsis are shown to synthesize chemoprotective aliphatic glucosinolates (AGS) and indolic glucosinolates (IGS), which are known for their biological activities against fungi, bacterial pathogens, or herbivores. UPLC/ESI-QTOF-MS analysis of various IGS mutants reveal increased or decreased levels of IGS in trichomes of gain- and loss-of-function mutants correspondingly. Using pMYB51/HIG1-uidA and pMYB28/PMG1/HAG1-uidA reporter plants we demonstrate that production of these important compounds is activated in trichomes of leaves or inflorescences in response to wounding. Since trichomes represent the first interface in plant-environment interactions, the possible role of GS containing trichomes in plant defense or signaling is discussed.

Elucidating the Role of Transport Processes in Leaf Glucosinolate Distribution

“…S3). However, glucosinolate content in trichomes was reported to represent 1% of the glucosinolate content in the remaining leaf (Frerigmann et al, 2012), whereas glucosinolate content in the abaxial epidermis in this study represents approximately 30% of the glucosinolate content in the remaining leaf, for both the wild type and gtr1gtr2 dKO (data not shown). This indicates a minimal influence of glucosinolates present in trichomes on the reported glucosinolate levels in epidermis peels.…”

“…A recent study reported that isolated Arabidopsis trichomes contain glucosinolates, mainly 4-MSB, 8-MSO, and I3M (Frerigmann et al, 2012). As trichomes were not removed before abaxial epidermis peeling in this study, glucosinolates from these may have contributed to glucosinolate levels observed in the epidermis ( Fig.…”

“…4-MTB, which is strongly allocated toward the abaxial epidermis (Supplemental Fig. S3), was not found in isolated trichomes (Frerigmann et al, 2012), indicating that this 4-MTB allocation is not due to a high concentration of this glucosinolate in trichomes.…”

“…Epidermis-derived trichomes have been shown to contain glucosinolates and supposedly also the glucosinolate biosynthetic machinery (Frerigmann et al, 2012), but it is currently not known whether the Arabidopsis leaf epidermis contains glucosinolates. As GTR1 has been localized to the epidermis (Nour-Eldin et al, 2012), it is plausible that this tissue could represent a GTR1-dependent glucosinolate sink within an Arabidopsis leaf.…”

“…A localization study of cyanogenic glucosides, defense molecules related to glucosinolates (Halkier and Gershenzon, 2006), determined that these compounds primarily were located in the epidermis of sorghum (Sorghum bicolor; Kojima et al, 1979). Whereas epidermis-derived trichomes in Arabidopsis were recently demonstrated to contain glucosinolates and to express glucosinolate biosynthetic genes (Frerigmann et al, 2012), no studies have investigated glucosinolates in the epidermal cell layer.…”