Changes in gene expression in response to altered SHL transcript levels.

The nuclear SHL protein is composed of a N-terminal BAH domain and a C-terminal PHD finger. Both domains are found in transcriptional regulators and chromatin-modifying proteins. Arabidopsis plants over-expressing SHL showed earlier flowering and senescence phenotype. To identify SHL regulated genes, expression profiles of 35S::SHL plants were established with Affymetrix ATH1 microarrays. About 130 genes showed reduced transcript levels, and about 45 genes showed increased transcript levels in 35S::SHL plants. The up-regulated genes included AGL20 and AGL9, which most likely cause the early flowering phenotype of 35S::SHL plants. Late-flowering SHL-antisense lines showed reduced AGL20 mRNA levels, suggesting that AGL20 gene expression depends on the SHL protein. The stronger expression of senescence- and defence-related genes (such as DIN2, DIN11 and PR-1 ) is in line with the early senescence phenotype of SHL- over-expressing plants. SHL-down-regulated genes included stress response genes and the PSR3.2 gene (encoding a beta-glucosidase). SHL over-expression did not alter the tissue specificity of PSR3.2 gene expression, but resulted in reduced transcript levels in both shoots and roots. Plants with glucocorticoid-inducible SHL over-expression were established and used for expression profiling as well. A subset of genes was identified, which showed consistent changes in the inducible system and in plants with constitutive SHL over-expression.