Isolation and characterization of three families of auxin down-regulated cDNA clones.

Five cDNA clones (ADR6, ADR11-1, ADR11-2, ADR12-1 and ADR12-2), representing three families of auxin down-regulated (ADR) genes were isolated and characterized. These were isolated by screening a lambda Zap cDNA library with the partial cDNA clones p6, p11 and p12, isolated earlier (Baulcombe and Key, J Biol Chem 255: 8907-8913, 1980). Hybrid-select translation of ADR6, ADR11-2 and ADR12-2 clones produced polypeptides of 33 kDa 22.5 kDa and a 6 and 7 kDa respectively, when analyzed by SDS-PAGE. ADR6 and ADR12-2 gave one and two spots, respectively, on an IEF-SDS 2D gel. ADR11-2 probably encodes a basic protein as it was only resolved on non-equilibrium pH gradient gel electrophoresis (NEPHGE). Genomic Southern blot analysis of ADR6, ADR11 and ADR12 suggests that each represents a small multigene family. The RNA levels corresponding to ADR6, ADR11 and ADR12 decrease in response to applied auxin by 100-, 15- and 10-fold, respectively (Baulcombe and Key, 1980). Runoff transcription, done in the presence and absence of auxin, showed that the rate of transcription of the genes corresponding to ADR6, ADR11-2 and ADR12-2 was reduced in the presence of auxin, but the decrease was small relative to the decrease in the cytoplasmic levels of these mRNAs, in response to auxin. A comparative analysis of the influence of auxin on in vitro transcription and steady state RNA levels corresponding to these ADR cDNAs suggests that the decrease in rate of transcription due to auxin is not enough to account for the auxin-induced decrease in the steady state levels. Northern analysis showed developmental and organ/tissue-specific response of these ADR genes. Furthermore, the expression of the genes corresponding to ADR6 and ADR12-1 appears to be up-regulated by light, whereas the gene corresponding to ADR11 appears to be down-regulated by light.