Abstract
A number of genetic studies have identified many shoot gravitropism mutants in Arabidopsis, leading to findings of proteins which are involved in gravitropic response. But details of gravity perception and later signal transductions still remain unknown. A transcriptional repressor MSG2/IAA19 is involved in auxin responses in Arabidopsis. To identify regulators of IAA19 expression, we performed screening of EMS mutagenized lines of IAA19promoter::NLS-GFP and IAA19promoter::GUS transgenic plants. We isolated a novel mutant of shoot gravitropism, A78. It showed lower GFP signal intensity than WT, and real-time PCR analyses confirmed this result though its auxin responsibility was kept intact. Although A78 phenotype resembled to the agravitropic mutant eal1 (Fujihira et al. 2000) which lacks endodermal amyloplasts in hypocotyls, A78 contained as many endodermal amyloplasts as WT. Genetic analyses revealed that A78 was a recessive mutation. We mapped this mutation in a novel gene in chr5. A T-DNA insertion mutation in this gene did not complement the gravitropic defects of A78. Furthermore, a T-DNA mutant of A78's paralog showed abonormal phenotypes including spiral leaf petioles.
