Data from: Synergy between RecBCD subunits is essential for efficient DNA unwinding

The subunits of the bacterial RecBCD act in coordination, rapidly and processively unwinding DNA at the site of a double strand break. RecBCD is able to displace DNA binding proteins, suggesting that it generates high forces, but the specific role of each subunit in the force generation is unclear. Here, we present a novel optical tweezers assay that allows monitoring the activity of RecBCD's individual subunits, when they are part of an intact full complex. We show that RecBCD and its subunits are able to generate forces up to 25-40 pN without a significant effect on their velocity. Moreover, the isolated RecD translocates fast, but is a weak helicase with limited processivity. Experiments at a broad range of [ATP] and forces suggest that RecD unwinds DNA as a Brownian ratchet, rectified by ATP binding, and that the presence of the other subunits shifts the ratchet equilibrium towards the post-translocation state

Interdependent Nutrient Availability and Steroid Hormone Signals Facilitate Root Growth Plasticity

International audiencePlants acquire essential elements from inherently heterogeneous soils, in which phosphate and iron availabilities vary. Consequently, plants have developed adaptive strategies to cope with low iron or phosphate levels, including alternation between root growth enhancement and attenuation. How this adaptive response is achieved remains unclear. Here, we found that low iron accelerates root growth in Arabidopsis thaliana by activating brassinosteroid signaling, whereas low-phosphate-induced high iron accumulation inhibits it. Altered hormone signaling intensity also modulated iron accumulation in the root elongation and differentiation zones, constituting a feedback response between brassinosteroid and iron. Surprisingly, the early effect of low iron levels on root growth depended on the brassinosteroid receptor but was apparently hormone ligand-independent. The brassinosteroid receptor inhibitor BKI1, the transcription factors BES1/BZR1, and the ferroxidase LPR1 operate at the base of this feedback loop. Hence, shared brassinosteroid and iron regulatory components link nutrient status to root morphology, thereby driving the adaptive response