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A novel HSI2 mutation in Arabidopsis affects the PHD-like domain and leads to derepression of seed-specific gene expression

Vijaykumar Veerappan, Jing Wang, Miyoung Kang, Joohyun Lee, Yuhong Tang, Ajay K. Jha, Huazhong Shi, Ravishankar Palanivelu and Randy D. Allen
Planta
Vol. 236, No. 1 (July 2012), pp. 1-17
Published by: Springer
Stable URL: http://www.jstor.org/stable/43564696
Page Count: 17
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A novel HSI2 mutation in Arabidopsis affects the PHD-like domain and leads to derepression of seed-specific gene expression
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Abstract

Two related B3 domain transcriptional repressore, HS12 (HIGH-LEVEL EXPRESSION OF SUGARINDUCIBLE GENE2)/VAL1 (VP1/AB13-LIKE1) and HSL1 (HS12-LIKE1)/VAL2, function redundantly to repress key transcriptional regulators of seed maturation genes in Arabidopsis thaliana seedlings. Using a forward genetic screen designed to isolate trans-acting mutants that affected expression of a transgene containing the glutathione 5-transferase F8 promoter: rluciferase (GSTF8::LUC reporter, we identified a novel HSI2 mutant allele, hsi2-4, that exhibits constitutively elevated luciferase expression while expression of the endogenous GSTF8 transcript remains unchanged. The hsi2-4 lesion was found to be a missense mutation that results in the substitution of a conserved cysteine within the plant homeodomain-like (PHD) motif of HSI2. Microarray analysis of hsi2-4 and hsi2-4 hsll mutants indicated that the HSI2 PHD-like domain functions non-redundantly to repress a subset of seed maturation genes, including those that encode AGL15 (AGAMOUS-LIKE15), FUSCA3 (FUS3), cruciferins, cupin family proteins, late-embryogenesis abundant protein, oleosins, 2S albumins and other seed-specific proteins in Arabidopsis seedlings. Many genes that are responsive to this mutation in the HSI2 PHD-like domain are enriched in histone H3 trimethylation on lysine 27 residues (H3K27me3), a repressive epigenetic mark. Chromatin immunoprecipitation analysis showed that sequences of the GSTF8::LUC transgene are enriched in H3K27me3 in a HSI2 PHD domain-dependent manner. These results indicate that the transcriptional repression activity of the HSI2 PHD domain could be mediated, at least in part, by its participation in the deposition of H3K27me3 on the chromatin of specific target genes.

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