Cellular Sand in the Gears

That small things can have a huge impact comes to no surprise to most modern scientists. After all, invisible (to our naked senses) things make up the universe. Pathogens of both humans and plants have devastated civilizations before we knew what bacteria and viruses even were. Similarly, a lot of small things can interfere with how a cell works.

This is the idea behind an October 2017 Plant Physiology paper “Identification of Novel Growth Regulators in Plant Populations Expressing Random Peptides”. It’s a pretty straight forward paper in a lot of ways. The scientists generated a series of small, random, peptides using some modern molecular biology techniques. Namely, the technology to build random sequences of DNA. They then introduced them into a lab plant, Arabidopsis, through genetic engineering and looked for effects on plant growth and development comparing normal plants to the GE ones.

As quick reminder of how life works: DNA  (made of the molecules – aka bases – one letter coded as A, T, G, and C) codes for its cousin molecule, RNA, that gets translated into proteins (that are strings of amino acids linked together in what is called a peptide chain – amino acids also all have their own on letter codes). Proteins do a majority of the work in any given cell and provide a lot of its structure. Each three letter combination codes for one amino acid. In this paper, Bao et al. created a random sequence of DNA of either 18 base pairs or 36 base-pairs that would code for 6 or 12 amino acid peptide chains (most proteins are 10’s to thousands of amino acids long).

The important thing about these peptides is their specific shape. Shape determines what locks they’ll fit into in the cell’s machinery. Bao et al. created GMO Arabidopsis plants, each expressing a lot of one of these random peptides. The scientists then looked for effects on plants that made them look different. They found one, dubbed PEP6-32 (for the 32nd peptide of 6 amino acids) mad the plants less able to sense red light. Another, PEP6-3, makes plants require external sucrose (table sugar) for them to grow normally (plants usually make enough sucrose on their own through photosynthesis).

F4.large
Figure 4 from Bao et al. 2017, showing four independent lines expressing PEP6-32. Note how normal plant’s (Col-0) respond to red light by elongating less and PEP6-32 plants have some blockage in the usual red light response. At right is the average length of hypocotyl. Source: Plant Physiology, See reference below for full citation.

Could these peptides be useful beyond a tool for plant scientists to use in gaining insights into how plants work by determining just how specific small peptides are changing a plants physiology? The answer is potentially yes, and not just as Genetically engineered organisms. These molecules are small enough, that some might be able to be sprayed on the soil or plants and be taken up inside the plant – or have their effect on the plant’s surface. Some might help manage pathogens, or effectively act as herbicides for weeds. PEP6-3 mentioned above makes plants require supplemental sugar. If that works by an external application, it could help kill weeds and favor crops in a field.

This is a relatively new approach and a pretty straight forward one to screen these peptides for any processes they may alter the function of. I wrote awhile ago about what are “microgenes” within larger genes that code for small peptides that change the level of RNA specific to the gene where they are encoded. It has been known for a long time that small peptides like CLAVATA3 (CLV3) effectively act as growth regulators, altering development, and keeping growth pattern regular. For example, at the heart of all plant organs is a meristem, a population of stem cells. These are maintained in part by a small peptide that gets cut out of a larger protein. A loss of CLV3 function leads to what is known as fasciation, or organ fusion.

These synthetic and random peptides open up a potentially new way to study plants’ biological processes as well as potentially generating new tools for agriculture.

References

Identification of Novel Growth Regulators in Plant Populations Expressing Random Peptides. Zhilong Bao, Maureen A. Clancy, Raquel F. Carvalho, Kiona Elliott, Kevin M. Folta. Plant Physiology Oct 2017, 175 (2) 619-627; DOI: 10.1104/pp.17.00577 (OA).

 


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