TOUCH INDUCES GENE EXPRESSION

 

 

 In nature, plants are challenged with hurricane winds, monsoon rains, and herbivore attacks, in addition to many other harsh mechanical perturbations that can threaten plant survival. As a result, over many years of evolution plants have developed very sensitive mechanisms through which they can perceive and respond to even subtle stimuli like touch. Some plants respond behaviorally to the touch stimulus within seconds, while others show morphological  alterations over a period of time ranging from days to week, such a gradual touch-induced morphological alterations are called Thigmomorphogenesis.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. But it is believed that various signaling molecules and phytohormones including intracellular calcium levels and some of the reactive oxygen species may have an implication in touch response.

 

Many genes are induced following touch (Braam and Davies, 1990). The signaling pathways and transcriptional mechanisms controlling the touch regulated gene expression are not well understood.  Intracellular calcium fluctuations and protein phosphorylation may play a role in touch regulated gene expression (Braam et al 1992).  A genome wide search of Arabidopsis genes sharing TCH regulatory properties was undertaken (Lee et al.,2005).  Hybridization of the 22,180 genes represented on the affimytrix DNA chip revealed that 589 genes, over 2.5% of the genome, are up-regulated at least twofold in expression within 30 min of a touch stimulation (Lee et al., 2005).  But how are these gene expressions induced. It is conjectured that a number of signaling molecules may play a role in between the stimuli of touch and the gene expression and the subsequent thigmomorphogenetic events.

 

Chehab et al. (2012) showed that Jasmonate (JA) a phytohormone is required for, and promotes, thigmomorphogenesis. JA deficient mutants did not respond to touch. Certain genes that are touch induced failed to be up regulated in this mutant, indicating that JA may mediate the stimulus transfer. However several other touch induced genes were unaffected suggesting perhaps the role of other signal molecules as well. 

 

 

REFERENCES:

 

Braam J.and Davis RW. (1990) Rain, Wind-Touch Induced expression of Calmodulin and Calmodulin related genes in Arabidopsis, Cell, 60:357-364

 

Braam et al. (1992) Regulated Expression of the calmodulin-related TCH genes in cultured Arabidopsis cells: Induction by Calcium and heat shock, Proceedings of the National Academy of Sciences, 89:3213-3216

 

Lee et al. (2005) Genome wide identification of Touch and darkness-regulated Arabidopsis genes: a focus on calmodulin-like and XTH genes, New Phytology, 165:429-444

 

Chehab et al. (2012) Arabidopsis touch induced morphogenesis is jasmonate mediated and protects against pest, Current Biology, 22:1-6