With the official start of Spring, many of us are starting to think about switching out our shovels and snow tires for soil and seeds. When planning a garden we often choose plants based on their food value or colorful petals. But how often do we take leaf shape into consideration? Leaves come in many varieties: silky, fuzzy, round, pointed, small, large, thin, thick, smooth, serrated, and a multitude of combinations of these traits. If you wanted to, you could make an elaborate garden just featuring plants with different leaf patterns.
So what controls the way leaves look?
One group of researchers recently published a paper describing why some plants have simple full leaves, while others form a branched leaf pattern. They looked at Arabidopsis thaliana, as an example of a plant with simple leaves, and Cardamine hirsuta, as an example of a plant with a more branched leaf pattern.
Simple-leafed and branched-leafed plants initially generate similarly shaped leaves. At some point though, something changes in the plants with branched leaves. Rather than maintaining a simple leaf pattern, these plants start to form leaflets. Up until recently, no one new what in the genetic code of these plants directed the shift to a branched leaflet pattern.
To address this question, the authors of the new paper compared the genomes of A. thaliana (simple leaves) and C. hirsuta (branched leaves) to each other and found a gene present in C. hirsuta that once existed in A. thaliana, but was lost over time. This gene, called rco for reduced complexity, had been shown to be responsible for the development of leaflets; mutating the gene so that it can no longer function causes C. hirsuta to form simple leaves instead of leaflets.
So what is rco? It belongs to the family of homeobox genes, which are critical to development across species. Humans have homeobox genes too; they control the correct formation of limbs and organs, and also act to prevent tumor development by preventing uncontrolled cell growth. If there are any X-Files fans out there, you may remember the episode “Post-Modern Prometheus” from the 5th season (the black-and-white episode that borrows from Frankenstein, and features a Cher sound track). At one point in the episode, researcher Dr. Pollidori discusses his research into fruit fly development, highlighted by his ability to make legs grow out of the flies’ heads.
Mulder: “Why would you do that?”
Dr. Pollidori: “Because I can.”
Dr. Pollidori was able to create those flies by altering expression of homeobox genes, thereby misdirecting where the legs should form. It’s worth mentioning these types of experiments have actually been done, and while perhaps a bit creepy in nature, they have led to our understanding of what homeobox genes do.
Back to the plants, the researchers found that the RCO protein (encoded by the rco gene) is present only in specific areas of developing C. hirsuta leaves, namely areas that form the base of leaflets. To confirm rco is responsible for directing leaf shape, they expressed it in A. thaliana to see if its leaves would retain their simple shape. As they expected, these transgenic A. thaliana plants formed deeply lobed leaves instead of their normal simple leaves. They also found that rco directs formation of leaflets by blocking growth in between leaflets; the halted growth causes the branched pattern in C. hirsuta. rco is not expressed only in C. hirsuta; it can be found in other plants as well. In fact the presence or absence of this gene has helped researchers better understand the evolutionary history and relationships of some plant species.
So the next time you’re trying to decide which plants to place in your garden or to brighten up your home, remember the intricacies and patterns aren’t located just in the petals. You may find those green leafy projections we often ignore have beauty of their own, directed by genes similar to those found in our own bodies.
Vlad, Daniela, et al. 2014. “Leaf Shape Evolution Through Duplication, Regulatory Diversification, and Loss of a Homeobox Gene.” Science. Vol 343. Pgs 780-783.
Keep An Open Mind – cosmedx science
It probably won’t come as a surprise that a Krishna Das CD of (non-traditional) kirtan chanting loses some of its calming effect when it skips. “Harreee Krisssshhhnaaaaaa” isn’t quite the same as, “Ha-ha-re-re-re-re Krish-ish-nn-nn-a.” If this had happened to my REO Speedwagon or Journey CD, I would have become annoyed on the spot. Instead, I laughed. Perhaps the CD, albeit having seen better days, hasn’t lost all of its magic yet.
I first heard about Krishna Das during a class on medical anthropology I took my senior year of college. This wound up being one of my favorite classes I took at Clark. I already had an interest in studying other cultures that started when I was a kid and stumbled upon documentaries on indigenous tribes throughout the world (REAL documentaries, before reality TV “documentaries” took over). This class fed right into my interest as we learned about holistic health practices like acupuncture, different types of meditation, and shamanism, as well as different perspectives on the body and health. Did you know that some cultures think we’re insane for centralizing sick people in one location, i.e., hospitals? Why send a sick person away from the comfort of their own home and family to be surrounded by other sick people? Interesting point.
The only problem I experienced with this class was the overwhelming guilt and confusion I felt over loving the material while also preparing for a career in scientific research. After all, acupuncture, meditation, and the like haven’t exactly been wholly accepted, or respected, by the broader scientific culture. So I hid my interest in and curiosity of holistic medicine and health practices, and found myself constantly fighting a mental war of how to reconcile liking these two desperately divergent areas. Did I need to choose one area over another? How? Which one was the “right” one?
I only recently have started coming to the realization that science and holistic medicine aren’t mutually exclusive. Clearly I chose science as a career path, although I’ve tried to keep my interest in alternative medicine alive on the side. Most people who know me don’t know about these interests; certainly the people I work with on a regular basis don’t know about them, though if they’re reading this I suppose they do now. But I’m okay with that. So what changed my view?
While I believe this applies to everyone, scientists especially need to be willing to keep their minds open. They need to be able to examine questions from multiple perspectives and consider alternative explanations if they hope gain the knowledge they chase, the knowledge that leads to an understanding of how our world works. Having “alternative” interests pulls me away from strict science and exercises a part of my brain that would otherwise, I feel, go unused. I wholeheartedly believe that being able to appreciate health and medicine from a perspective that varies widely from the perspective I hold while at my lab bench helps me to keep an open mind, and to think more broadly about my own work.
Plus, knowing about cultures other than your own is just cool.
It was while listening to Krishna Das on my drive home that the idea for this post came to me and started to take shape. Desperate to not forget it before I got home, I pulled over and took out my mini writing notebook I now have the habit of carrying around with me for these exact situations. With Krishna Das chanting (on a different, non-scratched CD), “Hare Krishna, Hare Krishna. Krishna Krishna, Hare Hare. Hare Ram, Hare Ram. Ram Ram, Hare Hare,” I outlined my thoughts while parked on the side of the road.
Always keep an open mind; you never know where your next inspiration could come from.