Arabidopsis Touch-Induced Morphogenesis Is Jasmonate Mediated and Protects against Pests

Abstract

Plants cannot change location to escape stressful environments. Therefore, plants evolved to respond and acclimate to diverse stimuli, including the seemingly innocuous touch stimulus [1-4]. Although some species, such as Venus flytrap, have fast touch responses, most plants display more gradual touch-induced morphological alterations, called thigmomorphogenesis [2, 3, 5, 6]. Thigmomorphogenesis may be adaptive; trees subjected to winds develop less elongated and thicker trunks and thus are less likely damaged by powerful wind gusts [7]. Despite the widespread relevance of thigmomorphogenesis, the regulation that underlies plant mechanostimulus-induced morphological responses remains largely unknown. Furthermore, whether thigmomorphogenesis confers additional advantage is not fully understood. Although aspects of thigmomorphogenesis resemble ethylene effects [8], and touch can induce ethylene synthesis [9, 10], Arabidopsis ethylene response mutants show touch-induced thigmomorphogenesis [11]; thus, ethylene response is nonessential for thigmomorphogenesis. Here we show that jasmonate (JA) phytohormone both is required for and promotes the salient characteristics of thigmomorphogenesis in Arabidopsis, including a touch-induced delay in flowering and rosette diameter reduction. Furthermore, we find that repetitive mechanostimulation enhances Arabidopsis pest resistance in a JA-dependent manner. These results highlight an important role for JA in mediating mechanostimulus-induced plant developmental responses and resultant cross-protection against biotic stress.

Plant response to touch affects the behaviour of aphids and ladybirds

“…Phytochemical responses in plants caused by wounding can also be activated by touching and lead to increased insect resistance (Smith 1988). Recent reviews have documented that most plants possess the ability to perceive and respond to touch (Braam 2005;Telewski 2006) by morphological (Liu et al 2007) and physiological adjustments (Chehab et al 2012). Touched maize plants in our study exhibited significant reductions in all tested morphological parameters except root weight (see Table 1.)…”

“…Activation of an early touch detection system in plants can be valuable if a defence is activated before herbivore arrival. Chehab et al (2012) proposed that mechanically stimulated plants may be primed for a defence manifesting enhanced resistance to pests. This may represent an advantage for touched plants to partially repel aphids and thus reduce potential feeding damage.…”

“…Thigmo responses have been observed in different plant species (Jaffe 1973) with the main focus on agricultural crops (Braam 2005). Plants with specialised sensory cells respond immediately (Forterre et al 2005), while other plants show visible morphological modifications induced by touching over longer periods of time, from days to weeks (Telewski 2006;Liu et al 2007;Chehab et al 2012).…”

Plant neighbor detection through touching leaf tips precedes phytochrome signals

“…Gene ontology (GO) analysis showed an overrepresentation of several defense-related processes and brassinosteroid (BR) signaling (Table S1). The defense hormone jasmonic acid (JA) has recently been associated with touch-induced morphogenesis (20). However, jasmonic acid mutants showed a wild-type response to continuous touching, as did mutants in various other hormonal pathways and shade-avoidance mutants (Fig.…”

“…S4 A and B). Recently, the hormone JA has been implicated in thigmomorphogenesis (20), but JA mutants showed a wild-type hyponastic response to continuous touch (Fig. S4 E and F).…”