Germostatin resistance locus 1 encodes a PHD finger protein involved in auxin‐mediated seed dormancy and germination

Summary Seed dormancy and germination are important physiological processes during the life cycle of a seed plant. Recently, auxin has been characterized as a positive regulator that functions during seed dormancy and as a negative regulator during germination. Through chemical genetic screenings, we have identified a small molecule, germostatin ( GS ), which effectively inhibits seed germination in Arabidopsis. GSR1 ( germostatin resistance locus 1 ) encodes a tandem plant homeodomain (PHD) finger protein, identified by screening GS ‐resistant mutants. Certain PHD fingers of GSR 1 are capable of binding unmethylated H3K4, which has been reported as an epigenetic mark of gene transcriptional repression. Biochemical studies show that GSR 1 physically interacts with the transcriptional repressor ARF 16 and attenuates the intensity of interaction of IAA 17/ ARF 16 by directly interacting with IAA 17 to release ARF 16. Further results show that axr3‐1 , arf10 arf16 are hyposensitive to GS , and gsr1 not only resists auxin‐mediated inhibition of seed germination but also displays decreased dormancy. We therefore propose that GSR 1 may form a co‐repressor with ARF 16 to regulate seed germination. Besides promoting auxin biosynthesis via upregulating expression of YUCCA1 , GS also enhances auxin responses by inducing degradation of DΙΙ‐ VENUS and upregulating expression of DR 5‐ GFP . In summary, we identified GSR1 as a member of the auxin‐mediated seed germination genetic network, and GS , a small non‐auxin molecule that specifically acts on auxin‐mediated seed germination.