Sumedha B S, Bangalore University
Through evolution, plants have developed complex molecular machineries to sense and respond to a variety of environmental stimuli. Some of these responses have been studied and characterized at the molecular level. Plant responses to mechanical stimuli are very varied. However, the mechanisms of response to touch, rain, wind, and bending, are just beginning to unfold. Some plants like Venus flytrap, Mimosa, and sundew have specialized sensory cells that help them rapidly respond to touch. In Arabidopsis, trichomes on leaf surface act as rapid touch sensors, triggering Ca2+ responses in neighboring cells.
Periodic mechanical stimulation of plants results in various morphological changes. Repeated mechanostimulation has been found to cause severe alterations in plant morphology. This includes pithiness, dwarfism, altered mechanical properties of the stem, improved anchorage strength of roots, delayed flowering, and reduced stomatal aperture. These are collectively called thigmomorphogenesis. These morphological changes provide mechanical safety to the plants against strong wind, anchorage failure, and stem breakage.
Mechanical stimulation has been found to improve plant performance in stressful conditions like pathogen attack, drought, cold, and salinity. Thus, mechanostimulation is gaining attention as a potential method for sustainable agriculture practices to improve food security.
The plant response depends on the frequency of exposures and intensity of mechanical load. Understanding the molecular mechanism of mechanoperception and thigmomorphogenesis is essential for its application in large-scale farming.
Molecular Mechanism:
Two major classes of molecules have been identified in mechanoperception. The mechanosensitive ion (MS) channel is the most prominent group. It converts mechanical cues into chemical signals. The mechanical force increases membrane tension, this causes conformational changes in the transmembrane domain. This generates an electric current followed by various biochemical responses.
The other group of mechanoreceptors is receptor-like kinases (RLKs), such as Feronia (FER). Feronia mutants showed altered root growth responses (like enhanced skewing, and reduced penetration ability) when exposed to mechanically challenging environments. In addition to this, hypo-osmotic shock and impaired Ca2+ signaling after touching were observed in the roots of feronia mutants. Calcium signaling also plays a central role in plant mechanotransduction. Calcium-dependent protein kinases and calcium-binding proteins also might be involved.
Although substantial studies have been carried out regarding mechanoperception, the molecular mechanism of thigmomorphogenesis of plants is just beginning to unfold
Results Of The Study:
In this study, researchers have compiled a wide type of mutants having roles in mechanosensitive signaling. This was based on literature searches and meta-analyses of large-scale datasets. These mutants were screened for altered molecular responses, and gene expression when stimulated by gentle brushing.
They identified calmodulin-binding transcriptional activator-CAMTA3. This is a previously unidentified positive regulator of touch-induced gene expression and touch-induced delay of flowering. It was found that Feronia is a strong repressor of JA-dependent touch responses. Further, they found that CAMTA3 co-operates with CAMTA1/2 to control touch-induced gene expression of JA-independent pathway genes like TCH2/4.
Transcriptional plant response was found to be associated with rapid induction and a steep decline. The highest expression for many touch-responsive genes is around 22-25min after treatment. The expression levels for the genes go down to almost preinduction levels by 40 min.
The rapid decrease in mRNA levels within 10-15 min suggests an active mechanism of mRNA degradation. The half-life of some touch-inducible transcripts after inhibition of RNA polymerase was much longer.
Researchers further looked for factors that may regulate this rapid mRNA decay. CCR4-associated factors Caf1a and Caf1b were induced by touch treatments. CCR4-CAF protein complexes were found to be involved in mRNA destabilization by removal of poly-A tail. These were reported to affect the de-adenylation of wound-induced transcripts.
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Reference:
- Darwish, Essam, Ritesh Ghosh, Abraham Ontiveros-Cisneros, Huy Cuong Tran, Marcus Petersson, Liesbeth De Milde, Martyna Broda et al. “Touch signaling and thigmomorphogenesis are regulated by complementary CAMTA3-and JA-dependent pathways.” Science Advances 8, no. 20 (2022): eabm2091.https://www.science.org/doi/10.1126/sciadv.abm2091
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Author Info:
Sumedha B S is pursuing MSc in Biotechnology. She is a proactive person with a positive attitude. She is skilled in laboratory techniques of Biotechnology and Microbiology. Her interests include Science communication, Bioinformatics, and Biopharma. She is looking for learning opportunities to build a career in the Biotechnology field. LinkedIn profile: https://www.linkedin.com/in/sumedhaprofile/
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