A Labor-saving and Repeatable Touch-force Signaling Mutant Screen Protocol for the Study of Thigmomorphogenesis of a Model Plant Arabidopsis thaliana

Summary

A gentle touch-force loading machine is built from human hair brushes, robotic arms and a controller. The hair brushes are driven by robotic arms installed on the machine and move periodically to apply touch-force on plants. The strength of machine-driven hair touches is comparable to that of manually applied touches.

Abstract

Plants responding to both intracellular and extracellular mechanical stimulations (or force signals) and develop special morphological changes, a called thigmomorphogenesis. In past decades, several signaling components have been identified and reported for being involved in the mechanotransduction (e.g., calcium ion binding proteins and jasmonic acid biosynthesis enzymes). However, the relatively slow pace of research in the study of force signaling or thigmomorphogenesis is largely attributed to two reasons: the requirement for laborious human hand-manipulated touch induction of thigmomorphogenesis and the force strength errors associated with people’s hand-touch. To enhance the efficiency of external force loading on a plant organism, an automatic touch-force loading machine was built. This robotic arm-driven hair brush touches provide a labor-saving and easily repeatable touch-force simulation, unlimited rounds of touch repetition and adjustable touch strength. This hair touch-force loading machine can be used for both large scale screening of touch-force signaling mutants and the phenomics study of plant thigmomorphogenesis. In addition, touch materials such as human hair, can be replaced with other natural materials like animal hair, silk threads and cotton fibers. The automated moving arms on the machine may be equipped with water sprinkling nozzles and air blowers to mimic the natural forces of rain drops and wind, respectively. By using this automatic hair touch-force loading machine in combination with the hand-performed cotton swab touching, we have investigated the touch response of two force signaling mutants, MAP KINASE KINASE 1 (MKK1) and MKK2 plants. The phenomes of the touch-force loaded wild type plants and two mutants were evaluated statistically. They have exhibited significant differences in touch response.

Introduction

Plant thigmomorphogenesis is a term that was coined by Jaffe, MJ in 1973¹. It is a plant tropism but different from the well-known phototropism or gravitropism caused by stimuli of sunlight or gravity^2,3. It describes phenotypic alterations associated with periodic mechanical stimulations, which have been frequently observed by botanists in earlier times^4,5. Raindrops, wind, plant, animal and human touches, even animal bites, are all considered to be different types of mechano-stimuli that trigger the force signaling in plants

Protocol

1. Seed preparation

NOTE: Arabidopsis seeds of both wild type (Col-0) as well as mkk1 and mkk2 loss-of-function mutants used were purchased from the Arabidopsis Biological Resource Center (ABRC, https://www.arabidopsis.org, Columbus, OH).

1. Calculate how many plant individuals of each genotype will be used for a reliable statistical analysis. Prepare a sufficient number of seeds based on the germination rate of each line, usually 4-5 times more than what is needed for an experiment. Ensure enough number of healthy and uniform-sized plants can be used for touch response assay. According to this protocol, ....

Results

The automatic hair touch-force loading machine
For observation of morphological changes on plants, both the reproducible growth conditions and treatment methods are key to obtaining repeatable results. This high-throughput and automatic touch-force signaling mutant screening is achieved by the newly built hair touch-force loading machine, Model K1 (Figure 1, Figure 2). These hair brushes can touch a maximum of 4 trays of plants simultaneousl.......

Discussion

Thigmomorphogenesis is a complex plant growth response towards mechanical perturbations, which involves a network of cellular signaling and action of phytohormones. It is a consequence of adaptive evolution of plants to survive under the undesirable environmental conditions^25,26. Mechanical touch, especially human finger touch and hand-held cotton swab touch, have been selected to study this morphological changes in previously thigmomorphogenetic studies

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
4 hair brushes		customized
4 robot arms with one holder		customized	1000 mm length holder and 560 mm length robot arm
57 stepper motor		57HS22-A
All purpose potting soil	Plantmate, Hong Kong
Arabidopsis plant seeds	Arabidopsis Biological Resource Centers, Columbus, OH		For arabidopsis seed purchase
BIO-MIX potting substratum	Jiffy Products International BV, the Netherlands	1000682050	Two soils were mixed together to grow Arabidopsis. The ratio of All purpos potting soil and  BIO-MIX is 1:2
IL 1700 research radiometer	International Light, Newburyport, MA		The light intensity of both full-wavelength and photosynthetic active radiation can be measured.
ImageJ	https://imagej.nih.gov/ij/download.html		Free downloaded software
Ju Feng Precision and Automation Technology Limited	Shenzhen, China		For belt-driven linear actuators and other mechanical modules purchase
Junction plate of the slide block			To fix the Y guide-rail module or Y auxiliary girder onto backs of slide blocks
Junction plate of the X axis module		customized	To connect the X guide-rail module and X auxiliary girder
Slide block
WDT4045 X axis guide-rail module		843 mm, customized	Pre-installed with two slide blocks and one 57 stepper motor
WDT4045 Y axis guide-rail module		1038 mm, customized	Pre-installed with two slide blocks and one 57 stepper motor
X axis auxiliary girder		843 mm, customized	Pre-installed with two slide blocks
Y axis auxiliary girder		1038 mm, customized	Pre-installed with two slide blocks