Figure 4.

Regulation of STAR1 and STAR2 by ART1.

(A) and (B) Relative expression levels of STAR1 (A) and STAR2 (B) in root tip (0 to 10 mm) of the wild type and art1 mutant treated with 0 to 50 μM Al, pH 4.5, or without Al, pH 5.6, for 6 h, were determined by quantitative RT-PCR. Expression relative to the wild type expression without Al treatment, pH 4.5, is shown. Data are means ± sd (n = 3).

(C) Yeast one-hybrid assay. A pair of plasmids, (1 to 4) pHIS-ProSTAR1 [HIS reporter gene with STAR1 promoter, containing a region between −939 (1), −629 (2), −436 (3), or −297 (4) to −172 from STAR1 start codon] and pGAD-ART1 (fusion of GAL4 activation domain and ART1), (NC1) pHIS2.1 (without STAR1 promoter) and pGAD-ART1, (NC2) pHIS-ProSTAR1 and pGADT7 (GAL4 activation domain only) were introduced into yeast strain Y187 and cultured on SD medium containing 0 or 20 mM 3-amino-1,2,4-triazole, a competitor of HIS3 at 30°C for 3 d in the absence of His.

(D) Relative Al sensitivity of art1, star1, and the art1 star1 double mutant. Five-day-old seedlings were exposed to a 0.5 mM CaCl₂ solution containing 0 or 5 μM Al, pH 4.5, for 24 h. Relative root elongation (root elongation with Al/root elongation without Al × 100) is shown. Data are means ± sd (n = 10). Different letters indicate significant differences at P < 0.05 by Student's t test.