Studies of ambient-pressure and high-pressure behavior of photoluminescence (PL) for series of InxAl1-xN layers are presented. The measured evolution of PL energy (E-PL) with x is characterized by a clear decrease of E-PL and exhibits a strong bowing. This dependence corresponds to the predictions of ab initio calculations of the band-gap energy changes E-G with x. However, values of E-PL are clearly lower than E-G, for 0<x<0.3. For higher x, the measured E-PL follows well the calculated E-G. The experimentally determined pressure coefficient of PL energy (dE(PL)/dp) shows a complicated behavior for alloys with different In-content. We found a strong reduction of dE(PL)/dp for 0<x<0.3 and a relatively constant magnitude of this coefficient for higher x. Moreover, for the lower x region, we observed dE(PL)/dp that can differ even by a factor two in samples with nominally very similar In-content. The general tendency in dE(PL)/dp evolution with x corresponds to lower values than calculated dE(G)/dp for alloys with non-uniform indium distribution. We propose two not necessary independent explanations of these experimental findings. First, due to non-uniform In distribution (induced, e. g. by defects or non-homogeneous strain) both E-PL and dE(PL)/dp are reduced. Second, a similar behavior results from an involvement of the localized states, whose formation and contribution to PL can be induced by strain and/or native defects. In both hypotheses, the strain/defect density can significantly change around x approximate to 0.18 where InxAl1-xN layers are lattice matched to GaN template. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim