The evolution of stomatal traits along the trajectory toward C4 photosynthesis

Abstract

C4 photosynthesis optimizes plant carbon and water relations, allowing high photosynthetic rates with low stomatal conductance. Stomata have long been considered a part of the C4 syndrome. However, it remains unclear how stomatal traits evolved along the path from C3 to C4. Here, we examined stomata in the Flaveria genus, a model used for C4 evolutionary study. Comparative, transgenic, and semi-in-vitro experiments were performed to study the molecular basis that underlies the changes of stomatal traits in C4 evolution. The evolution from C3 to C4 species is accompanied by a gradual rather than an abrupt change in stomatal traits. The initial change appears near the Type I intermediate stage. Co-evolution of the photosynthetic pathway and stomatal traits is supported. On the road to C4, stomata tend to be fewer in number but larger in size, and stomatal density dominates changes in anatomical maximum stomatal conductance (gsmax). Reduction of FSTOMAGEN expression underlies decreased gsmaxin Flaveria and likely occurs in other C4 lineages. Decreased gsmax contributes to the increase in intrinsic water use efficiency in C4 evolution. This work highlights the stomatal traits in the current C4 evolutionary model. Our study provides insights into the pattern, mechanism, and role of stomatal evolution along the road towards C4.

Speedy stomata of a C4 plant correlate with enhanced K+ channel gating

“…As expected, we observed lower rates of steady‐state transpiration, g s and higher WUE for G. gynandra when compared with Arabidopsis (Figures 1 and 2, Tables 1 and 2). These results reinforce much published work showing that many C 4 species achieve carbon assimilation with higher WUE and lower g s than related C 3 lineages (Israel et al, 2022; Osborne & Sack, 2012; Zhao et al, 2022). Unexpected, however, were the faster stomata movements in response light and CO 2 steps (Figure 3, Supporting Information S1: Figures and ) and the mismatch when comparing stomatal densities and size.…”

“…For example, Taylor et al (2012) observed among C 4 species a lower stomatal density compared with related C 3 species, but there was no significant difference in the size of the stomata. By contrast, a significant difference in density, size and stomatal length was reported between the C 4 and C 3 species within the genus Flaveria (Zhao et al, 2022), while among C 3 and C 4 grasses no differences were reported in stomatal size or density (Israel et al, 2022).…”

Midday water use efficiency in sorghum is linked to faster stomatal closure rate, lower stomatal aperture and higher stomatal density

“…In C 4 grasses, the relationship between SD and SS is weaker for species from drier habitats, such as sorghum, while the opposite is true for species from wetter environments (Taylor et al., 2012). From an evolutionary viewpoint, C 4 species present fewer, but larger, stomata, which contribute to their lower anatomical maximum stomatal conductance ( g smax ) than in their C 3 ancestors (Zhao et al., 2022). Stomatal pore size can also be physiologically adjusted by changing guard cell turgor (Hetherington & Woodward, 2003).…”

Rapid non-destructive method to phenotype stomatal traits

“…Conventional methods to phenotype stomata are time-consuming and costly, and do not allow screening large populations for beneficial stomatal traits. A commonly used method to investigate stomatal traits is a nail polish method (NP method) (10)(11)(12)(13)(14)(15). It consists of applying nail polish on the leaf surface to get a leaf imprint, waiting for the polish to dry, carefully pealing off the polish, examining the leaf imprint under a light microscope, taking and analysing images to determine stomatal traits.…”