Unveiling the deep plumbing system of a volcano by a reflection matrix analysis of seismic noise

In geophysics, volcanoes are particularly difficult to image because of the multi-scale heterogeneities of fluids and rocks that compose them and their complex non-linear dynamics. By exploiting seismic noise recorded by a sparse array of geophones, we are able to reveal the magmatic and hydrothermal plumbing system of La Soufri\`ere volcano in Guadeloupe. Spatio-temporal cross-correlation of seismic noise actually provides the impulse responses between virtual geophones located inside the volcano. The resulting reflection matrix can be exploited to numerically perform an auto-focus of seismic waves on any reflector of the underground. An unprecedented view on the volcano's inner structure is obtained at a half-wavelength resolution. This innovative observable provides fundamental information for the conceptual modeling and high-resolution monitoring of volcanoes.Comment: 32 pages, 9 figure

Bypassing Iron Storage in Endodermal Vacuoles Rescues the Iron Mobilization Defect in the Natural Resistance Associated-Macrophage Protein3natural Resistance Associated-Macrophage Protein4 Double Mutant

To improve seed iron (Fe) content and bioavailability, it is crucial to decipher the mechanisms that control Fe storage during seed development. In Arabidopsis (Arabidopsis thaliana) seeds, most Fe is concentrated in insoluble precipitates, with phytate in the vacuoles of cells surrounding the vasculature of the embryo. NATURAL RESISTANCE ASSOCIATED-MACROPHAGE PROTEIN3 (AtNRAMP3) and AtNRAMP4 function redundantly in Fe retrieval from vacuoles during germination. When germinated under Fe-deficient conditions, development of the nramp3nramp4 double mutant is arrested as a consequence of impaired Fe mobilization. To identify novel genes involved in seed Fe homeostasis, we screened an ethyl methanesulfonate-mutagenized population of nramp3nramp4 seedlings for mutations suppressing their phenotypes on low Fe. Here, we report that, among the suppressors, two independent mutations in the VACUOLAR IRON TRANSPORTER1 (AtVIT1) gene caused the suppressor phenotype. The AtVIT1 transporter is involved in Fe influx into vacuoles of endodermal and bundle sheath cells. This result establishes a functional link between Fe loading in vacuoles by AtVIT1 and its remobilization by AtNRAMP3 and AtNRAMP4. Moreover, analysis of subcellular Fe localization indicates that simultaneous disruption of AtVIT1, AtNRAMP3, and AtNRAMP4 limits Fe accumulation in vacuolar globoids

Control of seed coat rupture by ABA-INSENSITIVE 5 in Arabidopsis thaliana

In Arabidopsis, seed germination is a biphasic process involving rupture of the seed coat followed by emergence of the radicle through the micropylar endosperm. Embryo expansion results in seed coat rupture and removal of seed coat imposed dormancy with DELLA proteins blocking embryo expansion in the absence of gibberellins. Exogenous abscisic acid (ABA) treatment does not block seed coat rupture but does block radicle emergence. We used this limited effect of exogenous ABA to further investigate the mechanism by which it blocks the onset of germination marked by seed coat rupture. We show that physical nicking of the seed coat results in exogenous ABA treatment blocking both seed coat and endosperm rupture and this block requires the transcription factors ABI3 and ABI5, but not ABI4. Furthermore, we show that the repression of expression of several EXPANSIN genes (EXPA1, EXPA2, EXPA3, EXPA9 and EXPA20) by exogenous ABA requires ABI5. We conclude that ABI5 plays an important role in the ABA-mediated repression of germination through prevention of seed coat rupture and propose that this involves EXPANSIN related control of cell wall loosening

OPEN STOMATA3 - an ABC transporter implicated in ABA signalling, drought and light response

Mutants sensitive to progressive water deficit are characterized by excessive transpiration due to the failure of stomatal closure and can therefore be detected as cold plants (Fig. 1 blue) by remote infrared imaging (Merlot et al., 2002). Among the signalling mutants, three are collectively named open stomata (ost). The corresponding OST1 and OST2 genes encode an ABA-activated kinase and a P-type H+-ATPase, respectively (Mustilli et al., 2002; Merlot et al., 2007). The current work deals with OST3 which encodes an ATP-binding cassette (ABC) transporter. There are over 120 members of the ABC protein in the superfamily of Arabidopsis thaliana. Most of them are membrane-bound proteins that transport a diverse range of substances across the phospholipid bilayer. Characterisation of the mutant phenotype confirmed that ost3 transpires excessively (Fig. 1, 2). We have also shown that the ost3 mutations reduce seed dormancy (Fig. 3) but seed sensitivity to exogenous ABA seems unaffected (data not shown). The guard cells of ost3 are impaired in responses to ABA and light (Fig. 4), but are normal with respect to low level of CO2 which stimulates stomatal opening (data not shown). OST3 is expressed mainly in leaves, particularly in guard cells (Fig. 5), but it is low in root tissues. Transgenic expression of the OST3 protein fused to GFP in the ost3 mutant can rescue the phenotype and moreover, the fusion protein is targeted exclusively to the plasma membrane (Fig. 6) suggesting that it has a role in intercellular transport required for ABA signal perception. We found that OST3 interacts with OST2 (Fig. 8) and OST1 (Fig. 8 + 9). The last observation is also consistent with the fact that OST3 can be phosphorylated by OST1 in vitro (Fig. 7). Therefore we suggest that the trio of proteins identified by our genetic screen may function in the same signalling complex in mediating stomatal response

AtPUB19, a U-Box E3 Ubiquitin Ligase, Negatively Regulates Abscisic Acid and Drought Responses in Arabidopsis thaliana

Ubiquitination is an important protein post-translational modification, which is involved in various cellular processes in higher plants, and U-box E3 ligases play important roles in diverse functions in eukaryotes. Here, we describe the functions of Arabidopsis thaliana PUB19 (AtPUB19), which we demonstrated in an in vitro assay to encode a U-box type E3 ubiquitin ligase. AtPUB19 was up-regulated by drought, salt, cold, and abscisic acid (ABA). Down-regulation of AtPUB19 led to hypersensitivity to ABA, enhanced ABA-induced stomatal closing, and enhanced drought tolerance, while AtPUB19 overexpression resulted in the reverse phenotypes. Molecular analysis showed that the expression levels of a number of ABA and stress marker genes were altered in both AtPUB19 overexpressing and atpub19-1 mutant plants. In summary, our data show that AtPUB19 negatively regulates ABA and drought responses in A. thaliana