  Low-frequency radio arrays are opening a new window for the study of the sky,
both to study new phenomena and to better characterize known source classes.
Being flat-spectrum sources, blazars are so far poorly studied at low radio
frequencies.
  We characterize the spectral properties of the blazar population at low radio
frequency compare the radio and high-energy properties of the gamma-ray blazar
population, and search for radio counterparts of unidentified gamma-ray
sources.
  We cross-correlated the 6,100 deg^2 Murchison Widefield Array Commissioning
Survey catalogue with the Roma blazar catalogue, the third catalogue of active
galactic nuclei detected by Fermi-LAT, and the unidentified members of the
entire third catalogue of gamma-ray sources detected by \fermilat. When
available, we also added high-frequency radio data from the Australia Telescope
20 GHz catalogue.
  We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out
of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar
candidates. The mean low-frequency (120--180 MHz) blazar spectral index is
$\langle \alpha_\mathrm{low} \rangle=0.57\pm0.02$: blazar spectra are flatter
than the rest of the population of low-frequency sources, but are steeper than
at $\sim$GHz frequencies. Low-frequency radio flux density and gamma-ray energy
flux display a mildly significant and broadly scattered correlation. Ten
unidentified gamma-ray sources have a (probably fortuitous) positional match
with low radio frequency sources.
  Low-frequency radio astronomy provides important information about sources
with a flat radio spectrum and high energy. However, the relatively low
sensitivity of the present surveys still misses a significant fraction of these
objects. Upcoming deeper surveys, such as the GaLactic and Extragalactic
All-Sky MWA (GLEAM) survey, will provide further insight into this population.
