Within and between generation phenotypic plasticity in trichome density ofMimulus guttatus

Abstract

Mimulus guttatus (yellow monkeyflower) frequently produce glandular trichomes, a trait that may resist herbivory. Constitutive production of trichomes is variable both within and among populations of M. guttatus and most of this variation is genetic. This study demonstrates that damage on early leaves can induce increased trichome production on later leaves, a plastic response that is likely adaptive. Moreover, this study shows that this induction can be maternally transmitted, increasing trichome density in progeny before they experience herbivory. This transgenerational response must involve a yet undescribed epigenetic mechanism. These experiments also show genetic variation among plants in the capacity for both within and between plant generation induction. Despite the clear evolutionary importance of variation in constitutive and induced herbivory‐resistance traits, few other studies have noted genetic variation in both within a plant species.

The Genetics of Phenotypic Plasticity in Plant Defense: Trichome Production inMimulus guttatus

“…Trichome density is highly variable in M. guttatus, and its trichomes are straight and unicellular and occur in the glandular form, often secreting a sticky and potentially noxious fluid. Constitutive trichome density is variable both within and among populations of M. guttatus, and much of this variation is genetic (Holeski 2007a).…”

“…First, constitutive trichome density has been shown to reduce insect herbivore damage on M. guttatus plants, although this effect may depend on the local assemblage of both herbivores and their predators (J. Haloin, unpublished data). Second, damage similar to insect herbivory on early leaves induces plants to produce higher trichome densities on later leaves (Holeski 2007b). This response is more clearly consistent with a defensive function than with alternative drought-related hypotheses.…”

“…Several lines of evidence suggest that trichomes are a defensive trait in M. guttatus (see "Traits, Study Species, and Populations"). The Point Reyes population experiences relatively heavy herbivory, and its plants have high constitutive trichome densities (Holeski 2007a), whereas the Iron Mountain population experiences limited insect herbivory and its plants typically produce few trichomes. Our QTL mapping of trichome production directly tested ODT prediction that induction should be negatively correlated with constitutive defense.…”

“…Our mapping population was a large panel of recombinant inbred lines (RILs) derived from crossing two natural populations that are highly divergent for trichome density (Holeski 2007b). Several lines of evidence suggest that trichomes are a defensive trait in M. guttatus (see "Traits, Study Species, and Populations").…”

Jasmonic acid control of GLABRA3 links inducible defense and trichome patterning inArabidopsis

“…Wound-induced trichome formation has been reported in many plant species from diverse phylogenetic clades (Myers and Bazely, 1991;Agrawal, 1999;Traw and Dawson, 2002;Boughton et al, 2005;Holeski, 2007). It is known that the Myb-bHLH-WD40 complex is an evolutionarily conserved regulator of trichome development in Brassicaceae and Malvaceae, both of which belong to the Eurosid II clade of angiosperms (APG, 2003;Wang et al, 2004;Humphries et al, 2005;Gruber et al, 2006).…”