STIM1 and neoplasm: Although the synthesis of IAA by U. maydis is enhanced when maize plants are infected, the evidence that the IAA produced by U. maydis was involved in tumour formation was still minimal: U. maydis could still induce tumour formation despite the simultaneous knockout of four essential genes, tam1, tam2, iad1, and iad2, required for IAA biosynthesis (Doehlemann, Wahl, Vranes, et al., 2008; Reineke et al., 2008).