  Planet-disc interactions build up local pressure maxima that may halt the
radial drift of protoplanetary dust, and pile it up in rings and crescents.
ALMA observations of the HD135344B disc revealed two rings in the thermal
continuum stemming from ~mm-sized dust. At higher frequencies the inner ring is
brighter relative to the outer ring, which is also shaped as a crescent rather
than a full ring. In near-IR scattered light images, the disc is modulated by a
2-armed grand-design spiral originating inside the ALMA inner ring. Such
structures may be induced by a massive companion evacuating the central cavity,
and by a giant planet in the gap separating both rings, that channels the
accretion of small dust and gas through its filamentary wakes while stopping
the larger dust from crossing the gap. Here we present ALMA observations in the
J=(2-1)CO isotopologue lines and in the adjacent continuum, with up to 12km
baselines. Angular resolutions of 0.03" reveal the tentative detection of a
filament connecting both rings, and which coincides with a local discontinuity
in the pitch angle of the IR spiral, proposed previously as the location of the
protoplanet driving this spiral. Line diagnostics suggest that turbulence, or
superposed velocity components, is particularly strong in the spirals. The
12CO(2-1) 3-D rotation curve points at stellocentric accretion at radii within
the inner dust ring, with a radial velocity of up to ~6%+-0.5% Keplerian, which
corresponds to an excessively large accretion rate of ~2E-6M_sun/yr if all of
the CO layer follows the 12CO(2-1) kinematics. This suggests that only the
surface layers of the disc are undergoing accretion, and that the line
broadening is due to superposed laminar flows.
