Investigating the Specific Role of Sterols in Soybean Growth and Development
By Walter P. Suza, George Washington Carver Endowed Chair and adjunct associate professor of agronomy, ISU
Project Summary
Sterols are precursors to a vast array of signaling molecules such as steroid hormones in mammals and brassinosteroids (BR) in plants. Plants synthesize several sterols including campesterol, sitosterol, stigmasterol, and cholesterol (Schaller, 2003). In mammals, cholesterol is known to act as a signaling molecule and plays a vital role in early vertebrate development. Research in Arabidopsis has provided evidence that sterols are essential in plant growth and development. Campesterol is the direct precursor of BR, and several Arabidopsis sterol mutants show a dwarfed phenotype associated with BR deficiency. However, other sterol mutants show vascular patterning and embryonic defects that are not always rescued by exogenous application of BR. Further, there is striking variation in the levels of stigmasterol across different plant tissues, suggesting a specialized role in plant cell physiology (Suza and Chappell, 2016; Aboobucker and Suza, 2019). Taken together, these findings suggest that sterols have a role in plant development independent of BR.
The interaction of sterols with phospholipids helps maintain plasma membrane fluidity and permeability, particularly under stress (Grunwald, 1971; Hartmann, 1998). Plasma membrane fluidity serves as a critical stress sensor, with deviations triggering gene expression (Beney and Gervais, 2001). Moreover, sterols are associated with membrane proteins that govern oxidative stress, cellular signaling, and the uptake and transport of ions (Lefebvre et al., 2007). The conversion of sitosterol to stigmasterol during conditions of stress suggests that stigmasterol might modulate plasma membrane fluidity or signaling activities essential for plant growth and stress compensation. This idea is supported by studies showing that stigmasterol has a role in defense against bacterial pathogens and tolerance to extreme temperatures (Wang et al., 2012; Senthil-Kumar et al., 2013). In addition, treating germinating seeds with stigmasterol enhances salt tolerance in Faba beans and Flax (Hashem et al., 2011; Hassanein et al., 2012) and stigmasterol modulates the activity of the plasma membrane H+ -ATPase (Grandmougin-Ferjani et al., 1997). The plasma membrane H+ -ATPase is involved in transport of nutrients such as phosphorus (P) and adaptation to P deficiency in soybean (Michelet and Boutry, 1995; Shen et al., 2006).
The goal is to understand the role of stigmasterol in soybean growth and development. The objective is to identify the genes responsible for stigmasterol biosynthesis and explore their impact on soybean growth and development. Gene sequence analysis using the SoyBase database (Grant et al., 2010) points to two soybean candidate genes located in chromosome regions associated with flowering and pod maturity. To identify the genes involved in stigmasterol biosynthesis in soybean we plan to
- Measure stigmasterol content in soybean to understand how its profile changes during development and conditions of stress such as drought and salt.
- Quantify the mRNA expression levels of candidate genes and correlate their expression with stigmasterol content in various tissues.
- Validate candidate genes associated with the synthesis of stigmasterol by reducing their expression using the Virus Induced Gene Silencing (VIGS) technique. The VIGS vectors have already been developed in collaboration with Dr. Michelle Graham. Since stigmasterol might help soybean respond to stress, turning off stigmasterol production might result in plants that are more susceptible to abiotic stress.
- Evaluate VIGS plants with reduced stigmasterol for their growth and development including response to drought, salt, iron, and low P.
Additional Information
Describe the question, missing gap in knowledge, or problem being addressed or solved by the research.
There is a gap in our knowledge about control of stigmasterol biosynthesis and the sterol’s role in soybean growth and development. The research will help identify genes controlling the production of stigmasterol in a crop of economic importance and inform the design of gene-editing strategy to develop soybean with altered stigmasterol composition. The soybean stigmasterol mutants will serve as valuable tools for interrogating the specific role of plant sterols in responses to abiotic stress.
What do you expect to learn?
Preliminary data (not shown) from the collaboration with Graham’s lab suggest VIGS is a useful tool for reducing the expression of the candidate stigmasterol genes in soybean. The proposed research activities above will increase our knowledge about the specific role of sterols, and stigmasterol in particular, in plant growth and development.
Explain how this research will benefit a soybean farmer or the soybean industry.
In the longer-term, the research will identify soybean varieties with improved stigmasterol content that are better adapted to stress conditions. Given that low phosphorus levels pose a significant challenge in soybean cultivation (Wang et al., 2010), developing soybean varieties with elevated stigmasterol levels could potentially serve as a viable strategy for improving soybean production under phosphorus-limited conditions. Linking the proposed research with the George Washington Carver Future Hunger Fighters High School Outreach Program offers Iowa’s youth the chance to experience molecular biology research focused on a globally significant crop.
(2-year project funded fall 2024)