Senescence-Associated Gene Expression during Ozone-Induced Leaf Senescence in Arabidopsis1

Abstract

The expression patterns of senescence-related genes were determined during ozone (O3) exposure in Arabidopsis. Rosettes were treated with 0.15 μL L−1 O3 for 6 h d−1 for 14 d. O3-treated leaves began to yellow after 10 d of exposure, whereas yellowing was not apparent in control leaves until d 14. Transcript levels for eight of 12 senescence related genes characterized showed induction by O3. SAG13(senescence-associated gene), SAG21, ERD1(early responsive to dehydration), and BCB (blue copper-binding protein) were induced within 2 to 4 d of O3 treatment; SAG18, SAG20, and ACS6 (ACC synthase) were induced within 4 to 6 d; and CCH (copper chaperone) was induced within 6 to 8 d. In contrast, levels of photosynthetic gene transcripts,rbcS (small subunit of Rubisco) and cab(chlorophyll a/b-binding protein), declined after 6 d. Other markers of natural senescence, SAG12,SAG19, MT1 (metallothionein), andAtgsr2 (glutamine synthetase), did not show enhanced transcript accumulation. When SAG12promoter-GUS (β-glucuronidase) andSAG13 promoter-GUS transgenic plants were treated with O3, GUS activity was induced in SAG13-GUS plants after 2 d but was not detected in SAG12-GUS plants.SAG13 promoter-driven GUS activity was located throughout O3-treated leaves, whereas control leaves generally showed activity along the margins. The acceleration of leaf senescence induced by O3 is a regulated event involving many genes associated with natural senescence.