UW Department of Biology E-News
Summer 2012  |  Return to issue home

Challenging a Fine Balance

By Kristy Brady

Keiko Torii
Dr. Keiko Torii

Water availability was the major hurdle to plants colonizing land. Aquatic plants need no mechanism to conserve water, but inhabiting land further and further from a direct water source requires its prudent use. The planet’s first land plants – mosses, liverworts, and hornworts – were morphologically a small jump from their aquatic predecessors. They were tiny and restricted to damp, humid places. But land was a vast and unoccupied niche, so it didn’t take long for the evolutionary solution that would allow for land colonization to arise.

The cuticle, a waxy covering over the plant’s epidermis, prevents water from evaporating unchecked, thereby enabling water conservation. But the cuticle also prevents carbon dioxide from entering the plant and oxygen from leaving, a necessary exchange for photosynthesis to occur. Stomata, microscopic pores growing throughout a plant’s epidermis, solve this latter problem.

Confocal images from Torii's research
wt stomata
Wild type stomata
no-stomata mutant
No-stomata mutant
stomata-only mutant
Stomata-only mutant

Stomata are tightly regulated in both function and development. If there are too many, or they are open for too much of the time, a plant loses too much water resulting in dessication. Too few, or if they are not open enough, too little CO2 enters the plant, preventing photosynthesis. It’s a critical balance with implications not only for all plant life, but the atmosphere and biosphere, as well. Endowed Distinguished Biology professor and Howard Hughes Medical Institute and Gordon and Betty Moore Foundation Investigator Keiko Torii, is one of the leading researchers on the genetic control of stomatal patterning.

Broadly speaking, Torii is interested in how communities of cells communicate so that ultimately they develop into the right pattern, organ, or tissue. Between-cell communication is extraordinarily important, but it isn’t something most people think about regularly, and
that’s because most of the time things go right. But when cell-cell signaling fails, it’s often at a catastrophic level. Faulty communication between cells leads to a lack of coordination with the result being an amorphous, dysfunctional, and sometimes dangerous cell mass, i.e., a tumor.

Ten years ago very little was understood about plant stomatal development. Plant biologists had better understanding of the mechanism by which stomata functioned, that is, how guard
cells swelled and deflated to open or close the epidermal pore. But how stomata formed, and how they were arranged across a leaf’s surface, were still unsolved mysteries. Torii’s own research in this area transpired serendipitously. She was studying a group of receptor kinases,
a type of enzymes sensing external signals and transducing the signals inside of the cells via
phosphorylation, when a knock-out experiment yielded some interesting stomatal patterning
mutants. The mutants piqued Torii’s interest and she hasn’t looked back since. Additional
knock-out experiments identified additional players in the system, including several key
transcription factors that direct the cells to become stomata. Importantly, elements of the genetic
control of stomatal patterning that Torii has identified using the model plant Arabidopsis appear
to be highly conserved across all land plants.

This raises an interesting question: could stomatal patterning be manipulated for agricultural
purposes?

Water shortages are already a life-threatening problem in many regions of the world and climate
change is expected to amplify this problem in both frequency and severity, wrecking havoc on
agricultural production worldwide. Although water availability originally drove plant evolution
toward greater water conservation, it can’t happen fast enough this time to keep pace with the
combined agricultural pressures of a changing climate and growing population.

Torii’s research has identified the genetic controls for stomata density and spatial arrangement,
so represents an area of promising possible solutions. The question she is asking now is
whether it is possible to alter stomatal density without significantly compromising photosynthetic
capability and biomass production. For instance, she explains, if you could use 50% less water,
but still maintain 90% or more of your crop production, that would be a great start. Furthermore,
she says, some of the signals regulating stomatal formation are peptides, which means that in
theory they could be applied in the field in response to current or expected weather patterns.

The promise of Torii’s research is exactly why she was named an HHMI-GBMF Investigator last
year. It’s a prestigious honor and was awarded to only 15 scientists in the country. The goal of
the initiative was to support plant scientists conducting fundamental research that could possibly
find application in real world settings. And clearly the committee recognized the promise of
Torii’s research to exactly that. “More efficient water use is going to be critical in the future,”
Torii finished, “and hopefully some of the genes we’ve identified will help with that.”

This summer Torii was elected to the Washington State Academy of Sciences. The Washington
State Academy of Sciences provides expert scientific and engineering analysis to inform
public policy-making, and works to increase the role and visibility of science in the State of
Washington.

For more information about Keiko Torii’s research, visit her website: http://faculty.washington.edu/
ktorii/
and HHMI Bulletin: http://www.hhmi.org/bulletin/may2012/upfront/torii_stomata.html

 

Summer 2012  |  Return to issue home