Deep sea survey of Reunion Island continental slopes usin a R.O.V system - ABYSSEA expedition

A field survey conducted with a R.O.V. submarine system has been carried out for the first time between 100 and 400 m deep on the volcanic slopes of Reunion Island. 20 dives were conducted in the south-east of the island on the recent volcanic lava flows, and 13 dives were conducted in the west coast, associated with older geological substrates. Pillow-lavas have been recorded at a depth of 250 m on the 2007 lava flows, proving that the lava has burst at these depths, causing disturbance in the depths and up to several miles around. Pebble conglomerates were also observed in the north-west, in St-Paul Bay, between 100 and 200 m in depth, connecting to Rivière des Galets alluvial cone. Big collapses show that the substrate remains unstable in this area at deep depth. Concerning the communities, we have made an inventory of many species and more particularly 66 species of fish, 16 species of cnidarian, 8 species of arthropods and 7 species of echinoderms. Some of them have never before been observed in Reunion IslandUne exploration sous-marine à l'aide d'un engin de type R.O.V a été menée pour la première fois entre 100 et 400 m de profondeur sur les reliefs volcaniques de l'île de la Réunion. 20 plongées ont été effectuées dans le sud-est de l'île sur les coulées récentes et 13 dans l'ouest sur un substrat plus ancien. Des pillow-lavas ont ainsi été observées à 250 m sur les coulées volcaniques de 2007 prouvant que la lave a fait irruption sous l'eau, occasionnant des perturbations importantes en profondeur et sur des kilomètres aux alentours. Des conglomérats de galets ont également été découverts au nord-ouest, en baie de St-Paul, entre 100 et 200 m, révélant probablement la présence de la sédimentation ancienne du cône de déjection de la Rivière des Galets. De gros basculements de ces formations témoignent d'une instabilité, d'âge indéterminé, des dépôts à cette profondeur. Concernant les peuplements, de nombreuses espèces ont été recensées. Parmi les mieux représentées, 66 espèces de poissons ont été inventoriées, 16 de cnidaires, 8 d'arthropodes et 7 d'échinodermes. Certaines n'avaient encore jamais été observées à la Réunion

The pea branching RMS2 gene encodes the PsAFB4/5 auxin receptor and is involved in an auxin-strigolactone regulation loop

Strigolactones (SLs) are well known for their role in repressing shoot branching. In pea, increased transcript levels of SL biosynthesis genes are observed in stems of highly branched SL deficient (ramosus1 (rms1) and rms5) and SL response (rms3 and rms4) mutants indicative of negative feedback control. In contrast, the highly branched rms2 mutant has reduced transcript levels of SL biosynthesis genes. Grafting studies and hormone quantification led to a model where RMS2 mediates a shoot-to-root feedback signal that regulates both SL biosynthesis gene transcript levels and xylem sap levels of cytokinin exported from roots. Here we cloned RMS2 using synteny with Medicago truncatula and demonstrated that it encodes a putative auxin receptor of the AFB4/5 clade. Phenotypes similar to rms2 were found in Arabidopsis afb4/5 mutants, including increased shoot branching, low expression of SL biosynthesis genes and high auxin levels in stems. Moreover, afb4/5 and rms2 display a specific resistance to the herbicide picloram. Yeast-two-hybrid experiments supported the hypothesis that the RMS2 protein functions as an auxin receptor. SL root feeding using hydroponics repressed auxin levels in stems and down-regulated transcript levels of auxin biosynthesis genes within one hour. This auxin down-regulation was also observed in plants treated with the polar auxin transport inhibitor NPA. Together these data suggest a homeostatic feedback loop in which auxin up-regulates SL synthesis in an RMS2-dependent manner and SL down-regulates auxin synthesis in an RMS3 and RMS4- dependent manner