Development and Physiology of the Stomatal Complex in Grasses

Water is an increasingly scarce resource for agriculture thus engineering plants that use water efficiently is a primary goal forscientists. A recent approach in achieving water-efficient crops is to breed or engineer plants that can rapidly open and close their stomata in changing environments (Lawson and Blatt 2014, Raven 2014). During the day, plants may become shaded or enjoy a sudden but transient increase in sunlight as sun angles change (or are reflected) or as clouds and/or other obstacles block the sun. Plants that are shaded cannot photosynthesize; if the stomata are open in the shade, water is being lost while no carbon assimilation is taking place. Reciprocally, a transient increase in sunlight may warrant rapid stomatal opening, so extra energy can be assimilated into carbon. This is apt to happen many times a day, on different regions of the plant. Therefore, stomata that open quickly during high light or close quickly during low light will assimilate more carbon while losing less water. Interestingly, nature has already engineered rapid stomata. Within the plant family, grass stomata have a unique morphology. In
grasses, guard cells are dumbbell-shaped rather than the more common kidney-shape. The pair of guard cells are laterally flanked by a pair of subsidiary cells, or helper cell, which are also uniquely shaped (Figure 1C; Gray et al., 2020). Grass stomata open and close much faster than stomata from a variety of other species (Johnsson et al. 1976, Grantz and Assmann 1991, Franks and Farquhar 2007). It is thought that both the shape of the guard cells, and the presence of the subsidiary cellscontribute to this rapid opening and closing (Franks and Farquhar 2007; Gray et al., 2020; Raissig et al., 2017), however since the mechanism of rapid stomatal opening and closing in grasses is not well understood, this is yet unproven. Maize (corn) plants are members of the grass family. Maize has many features that make it amenable to study include: well-established genetics including characterized "diversity panels" of inbred lines, fully sequenced genomes from multiple inbred lines and reverse genetic collections; ability to make transgenic plants; and large cells amenable to microscopy.
Therefore, experiments in maize are well poised to investigate grass stomatal formation and function. While the unique shape of grass guard cells likely contributes to their function, this proposal will focus on subsidiary cells. Specifically, we will determine the genes required to form subsidiary cells and genes unique in mature functioning subsidiary cells.