Summary
We conducted an infrared thermal imaging‐based genetic screen to identify Arabidopsis mutants displaying aberrant stomatal behavior in response to elevated concentrations of CO
2.This approach resulted in the isolation of a novel allele of the Arabidopsis BIG locus (At3g02260) that we have called CO
2
insensitive 1 (cis1).
BIG mutants are compromised in elevated CO
2‐induced stomatal closure and bicarbonate activation of S‐type anion channel currents. In contrast with the wild‐type, they fail to exhibit reductions in stomatal density and index when grown in elevated CO
2. However, like the wild‐type, BIG mutants display inhibition of stomatal opening when exposed to elevated CO
2. BIG mutants also display wild‐type stomatal aperture responses to the closure‐inducing stimulus abscisic acid (ABA).Our results indicate that BIG is a signaling component involved in the elevated CO
2‐mediated control of stomatal development. In the control of stomatal aperture by CO
2, BIG is only required in elevated CO
2‐induced closure and not in the inhibition of stomatal opening by this environmental signal. These data show that, at the molecular level, the CO
2‐mediated inhibition of opening and promotion of stomatal closure signaling pathways are separable and BIG represents a distinguishing element in these two CO
2‐mediated responses.
Diverse bacterial species produce extracellular contractile injection systems (eCISs). Although closely related to contractile phage tails, eCISs can inject toxic proteins into eukaryotic cells. Thus, these systems are commonly viewed as cytotoxic defense mechanisms that are not central to other aspects of bacterial biology. Here, we provide evidence that eCISs appear to participate in the complex developmental process of the bacterium Streptomyces coelicolor. In particular, we show that S. coelicolor produces eCIS particles during its normal growth cycle, and that strains lacking functional eCIS particles exhibit pronounced alterations in their developmental program. Furthermore, eCIS-deficient mutants display reduced levels of cell death and altered morphology during growth in liquid media. Our results suggest that the main role of eCISs in S. coelicolor is to modulate the developmental switch that leads to aerial hyphae formation and sporulation, rather than to attack other species.
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