How improved valves let grasses 'breathe,'cope with climate change16 March 2017

This image shows the four-celled stomata found ingrasses, featuring two dumbbell-shaped guard cellssurrounded by two subsidiary cells. Scientists attributethe tremendous success of grasses to this valvestructure, which is capable of more-sensitive and preciseresponsiveness to the environment and likely enhancesthe plant's performance, particularly in hightemperatures or drought conditions. Credit: DominiqueBergmann and Michael Raissig

New work from a joint team of plant biologists andecologists from Carnegie and Stanford Universityhas uncovered the factor behind an importantinnovation that makes grasses—both the kind thatmake up native prairies and the kind we'vedomesticated for crops—among the most-commonand widespread plants on the planet. Their findingsmay enable the production of plants that performbetter in warmer and dryer climate conditions, andare published by Science.

All land plants take in carbon dioxide (CO2) fromthe atmosphere and "exhale" oxygen and watervapor. This exchange is required for plant growth;

the carbon dioxide is made into sugars byphotosynthesis, the process by which plants turnthe sun's energy into food. But it also is a majordriver of global climate cycles.

A plant needs to balance its ability to take in CO2with the potential to lose water. To achieve thisbalance it uses tiny, cellular valve-like pores on thesurfaces of its leaves called stomata (after theGreek word for mouths). In grasses, these valvesare particularly well-tuned; they can open wide tomaximize CO2 uptake and shut down quickly whenthe surrounding conditions would lead to increasedwater loss.

Because grass crops like corn, wheat, and rice area major food source, the Carnegie-Stanford groupwanted to know why the stomata in these particularplants work so much better than stomata in otherplants. One obvious feature is that in most plants,stomata are made up of just two so-called "guardcells", but grasses have an additional pair of cellson either side, which are called "subsidiary cells."These subsidiary cells enable the guard cells toopen and close especially quickly.

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This image shows mutant grass that's lacking theBdMUTE gene, which is responsible for the four-celledstomatal architecture normally found in grasses. In thismutant, a two-celled stomatal valve develops instead,which is much less efficient. Credit: DominiqueBergmann and Michael Raissig

In addition, while the guard cells of many plantshave a kidney shape, grass guard cells are anunusual "dumbbell" shape. The subsidiary cellsalongside these dumbbell-resembling cells providea mechanical boost to enable them to open wide.

In this study, led by Dominique Bergmann, anhonorary adjunct staff member at Carnegie'sDepartment of Plant Biology and Professor atStanford University's Biology Department, theresearchers used a relative of wheat calledBrachypodium to demonstrate that all grassstomata with a four-cell configuration, including thetwo subsidiary cells, are indeed more responsive tochanging environmental conditions, and have awider range of apertures for pore opening andclosing. This sensitivity likely enhances the plant'sperformance, particularly in high temperatures ordrought conditions.

Furthermore, the team—including lead authorMichael Raissig of Stanford and Carnegie GlobalEcology's Acting Director Joseph Berry—usedsophisticated research techniques to identify aspecific gene that enables Brachypodium to formthe lateral subsidiary cells. The gene, calledBdMUTE, encodes a protein that is considered a"master regulator" of cell behavior by turning onand off other genes that give cells their uniqueproperties. Without this master regulator,Brachypodium stomata resemble the more primitivetwo-celled stomata found in other plants, and theresearch team showed that grasses with these two-celled stomata perform poorly.

What was particularly interesting and surprising isthat BdMUTE isn't a brand-new protein found onlyin the grasses. Rather, it is a slightly modifiedversion of protein that, a decade ago, was shown tohave a different role in making two-celled stomatain the broadleaf mustard plant Arabidopsis. Whenan Arabidopsis cell is exposed to this version of the

MUTE protein, it gets the message that it shouldcommit itself to making guard cells. InBrachypodium, however, the protein moves out ofthe guard cell precursors into the neighbor cellsand then induces these neighbors to becomesubsidiary cells in the four-celled complex.

"Could the mobility of the grass version of MUTE bethe key to this master regulator's ability to set upthese physiologically improved, four-celled grassstomata?" Raissig asked.

"And could this finding be utilized to make cropsmore resistant to warm climates and water-scarceconditions?" added Bergmann. "This presents aninteresting target for further research that aims atengineering stomatal form and function to helpcrops cope in a changing climate, and ultimately,provide food for our ever-growing population."

The protein in yellow moves out of the guard cells intocells on both sides. By recruiting these cells, grassstomata become better suited to hot and dryenvironments. Credit: Michael Raissig and DominiqueBergmann

"This elegant work from Dominique and colleagues

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is a beautiful illustration of how plants evolveddevelopmental solutions to tackle physiologicalproblems." said Sue Rhee, Director of Carnegie'sPlant Biology.

More information: Michael T. Raissig et al.Mobile MUTE specifies subsidiary cells to buildphysiologically improved grass stomata, Science(2017). science.sciencemag.org/cgi/doi …1126/science.aal3254

Provided by Carnegie Institution for ScienceAPA citation: How improved valves let grasses 'breathe,' cope with climate change (2017, March 16)retrieved 14 January 2022 from https://phys.org/news/2017-03-valves-grasses-cope-climate.html

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