  We point out that protoplanets created in the framework of the Tidal
Downsizing (TD) theory for planet formation play a very important role for the
evolution of accretion discs hosting them. Since all TD protoplanets are
initially as massive as $\sim 10$ Jupiter masses, they are able to open very
deep gaps in their discs, and even completely isolate the inner disc flows from
the outer ones. Furthermore, in contrast to other planet formation theories, TD
protoplanets are mass donors for their protostars. One potentially observable
signature of planets being devoured by their protostars are FU Ori like
outbursts, and episodic protostar accretion more generally, as discussed by a
number of authors recently.
  Here we explore another observational implication of TD hypothesis: dust poor
inner accretion flows, which we believe may be relevant to some of the observed
mm-bright transitional discs around protostars. In our model, a massive
protoplanet interrupts the flow of the outer dust-rich disc on its protostar,
and at the same time looses a part of its dust-poor envelope into the inner
disc. This then powers the observed gas-but-no-dust accretion onto the star.
Upon a more detailed investigation, we find that this scenario is quite natural
for young massive discs but is less so for older discs, e.g., those whose
self-gravitating phase has terminated a fraction of a Million year or more ago.
This stems from the fact that TD protoplanets of such an age should have
contracted significantly, and so are unlikely to loose much mass. Therefore, we
conclude that either (i) the population of "transition discs" with large holes
and dust-poor accretion is much younger than generally believed; or (ii) there
is a poorly understood stage for late removal of dust-poor envelopes from TD
planets; (iii) another explanation for the observations is correct.
