Light affects plant growth and development throughout the life cycle. However, light signals de not function autono.
mously but should be integrated with endogenous developmental factors such as the plant hormone auxin to specify
correct developmental decisions. We have previously reported that the Arabidopsis shy2-1D mutation alters various
light responses, including highly photomorphogenic development in darkness. Here we show that the mutation also
alters various auxin responses, including constitutive formation of lateral roots and reduced auxin sensitivity in inhibition
of hyl)ocotyl and root growth. The mutation is a gain of function mutation occuring in the IAA3 8ene, one of the
Aux/IAA family genes encoding putative transcription factors of auxin-responsive genes. These results suggest that
IAA3/SHY2 may play important roles in both light- and auxin-mediated developmenL Considering that Aux/IAA proteins
and auxin response transcription factors interact with one another, we propose that IAA3/SHY2 may integrate
light signals into auxin-mediated developmental responses.