Plants optimize carbon assimilation while limiting water loss by adjusting stomatal aperture. In grasses, a developmental innovation—the addition of subsidiary cells (SCs) flanking two dumbbell-shaped guard cells (GCs)—is supposedly linked to the grass family's improved stomatal gas exchange efficiency. A mutant screen in the wheat relative and model grass Brachypodium distachyon identified a transcription factor necessary and sufficient for SC formation. Unexpectedly, the transcription factor is an ortholog of the stomatal regulator AtMUTE, which defines GC precursor fate in Arabidopsis. The novel role of BdMUTE in specifying lateral SCs appears linked to its acquisition of cell-to-cell mobility in Brachypodium. Physiological analyses on bdmu te mutant plants lacking SCs experimentally support classic hypotheses that SCs permit greater stomatal responsiveness to enhance water use efficiency and larger range of pore apertures to increase photosynthetic capacity. Recently, we profiled the transcriptome of developing and mature leaf regions of both wild-type and SC-less bdmute plants to identify novel factors regulating SC development and SC function, respectively. Discovering genes required for SC function will help understand how SCs actually improve stomatal gas exchange dynamics in grasses. Understanding how SCs are formed and enable grasses to breathe more efficiently might allow engineering of stomatal properties in many different crops to improve water use efficiency and plant performance.
Raissig, M. T.^, Matos, J. L., Gil, M. X. A., Kornfeld, A., Bettadapur, A., Abrash, E., et al. (2017). Mobile MUTE specifies subsidiary cells to build physiologically improved grass stomata. Science, 3 55(6330), 1215–1218. http://doi.org/10.1126/science.aal3254
Raissig, M. T.*, Abrash, E.*, Bettadapur, A., Vogel, J. P., & Bergmann, D. C. (2016). Grasses use an alternatively wired bHLH transcription factor network to establish stomatal identity. Proc Natl Acad Sci USA, 113(29), 8326-8331. http://doi.org/10.1073/pnas.1606728113