Transcriptional regulators involved in responses to volatile organic compounds in plants

Abstract

Edited by Joseph M. JezField studies have shown that plants growing next to herbivore-infested plants acquire higher resistance to herbivore damage. This increased resistance is partly due to regulation of plant gene expression by volatile organic compounds (VOCs) released by plants that sense environmental challenges such as herbivores. The molecular basis for VOC sensing in plants, however, is poorly understood. Here, we report the identification of TOPLESS-like proteins (TPLs) that have VOC-binding activity and are involved in VOC sensing in tobacco. While screening for volatiles that induce stress-responsive gene expression in tobacco BY-2 cells and tobacco plants, we found that some sesquiterpenes induce the expression of stress-responsive genes. These results provided evidence that plants sense these VOCs and motivated us to analyze the mechanisms underlying volatile sensing using tobacco as a model system. Using a pulldown assay with caryophyllene derivative-linked beads, we identified TPLs as transcriptional co-repressors that bind volatile caryophyllene analogs. Overexpression of TPLs in cultured BY-2 cells or tobacco leaves reduced caryophyllene-induced gene expression, indicating that TPLs are involved in the responses to caryophyllene analogs in tobacco. We propose that unlike animals, which use membrane receptors for sensing odorants, a transcriptional co-repressor plays a role in sensing and mediating VOC signals in plant cells.For terrestrial animals, odorants or volatile organic compounds (VOCs) 5 possess important biological and ecological information such as food, predator, and species. Sensing these chemical cues, animals take appropriate behavior such as attraction or avoidance, ensuring their survival. Plants also have to acquire information from the external environment and take appropriate action for survival. Defense or stress-related genes are up-regulated upon exposure to specific VOCs to prepare for environmental change in plants (1-4). For example, defense genes are induced in healthy lima bean leaves upon exposure to VOCs from infested leaves, but not from healthy or artificially wounded leaves (5). In addition, VOCs released from infested leaves prime neighboring plants for direct and indirect defense against future herbivore attack (6). VOCs are also used as cues for host selection and location by parasitic plants (7). Several individual compounds from host plants also show attractiveness to parasitic plants. Regardless of accumulated evidence for the VOC effects in plants, a molecular basis for the VOC detection by plant cells has not been revealed.In animals, VOCs are recognized by odorant receptors in the olfactory neural system that constitutes the largest G protein-coupled receptor (GPCR) family. In contrast, plants have only a few GPCR genes that appear to have different functions (8). It has been unclear how VOCs are sensed and the information is converted to signals that induce the specific responses in plant cells at the level of receptors. It is possible that plants have a...

The role of volatiles in plant communication

“…Indeed, the first response to volatiles that can be measured in plants is a change in plasma membrane potential and cytosolic calcium flux (Zebelo et al ., ). Very recently, the transcriptional co‐repressor TOPLESS‐like (TPL) protein was identified to bind volatile sesquiterpenes, that is caryophyllene analogues (Nagashima et al ., ). TPL proteins are known to regulate various hormonal responses such as those induced by jasmonic acid (Pauwels et al ., ).…”

Plant volatiles as cues and signals in plant communication

“…The study system used tobacco plants and a BY-2 cell culture. Cell culture experiments showed that overexpression of TPLs reduced the caryophyllene-induced gene expression (Nagashima et al, 2019).…”

“…The first is that β-caryophyllene binds TPL, releasing an unknown co-factor, which itself inhibits transcription factors when bound to TPL. The secondary mechanism by which β-caryophyllene could induce expression of NtOsmotin is by binding TPL competitively, preventing it from binding to the unknown co-factor (Nagashima et al, 2019). (Vivaldo et al, 2017).…”

“…An increased understanding of these mechanisms would enable discrimination between volatile cues and signals and their specified roles in plant–plant interactions. One protein involved in this VOC binding has recently been identified as a TOPLESS‐like protein (TPL) (Nagashima et al, 2019) (Figure 3F). The VOC involved in this study was β‐caryophyllene, which showed activity as a transcriptional co‐repressor.…”

Caterpillar-induced rice volatiles provide enemy-free space for the offspring of the brown planthopper

“…They also play a role in repelling herbivores that avoid inducible plant defenses and conspecific or heterospecific competition ( De Moraes et al, 2001 ; Knolhoff and Heckel, 2014 ; Anderson et al, 2011 ; Jiao et al, 2018 ) or they can attract specialist herbivores that aggregate to collectively overcome the defense of their hosts ( Loughrin et al, 1995 ; Weed, 2010 ; Robert et al, 2012 ). HIPVs can also be detected by neighboring plants and help them to anticipate an incoming attack ( Arimura et al, 2000 ; Heil and Ton, 2008 ; Engelberth et al, 2004 ; Karban et al, 2014 ; Sugimoto et al, 2014 ; Nagashima et al, 2018 ). Hence, HIPVs provide information to all players in a plant’s ecological network and through these various effects, HIPVs play a major role in determining the composition of insect communities in the field ( Xiao et al, 2012 ; Zhu et al, 2015 ; Poelman and Dicke, 2014 ; Blubaugh et al, 2018 ; Schuman and Baldwin, 2018 ).…”