biologia plantarum

Biologia plantarum 54:279-284, 2010 | DOI: 10.1007/s10535-010-0049-4

The lack of plastidal transit sequence cannot override the targeting capacity of Bradyrhizobium japonicum δ-aminolevulinic acid synthase in transgenic rice

K. Back¹, S. Jung^2,*

¹ Agricultural Plant Stress Research Center, Biotechnology Research Institute, Chonnam National University, Gwangju, Korea

² School of Life Sciences and Biotechnology, Kyungpook National University, Daegu, Korea

The δ-aminolevulinic acid synthase (ALA-S) is an enzyme which catalyzes the synthesis of δ-aminolevulinic acid (ALA). The Bradyrhizobium japonicum ALA-S coding sequence lacking plastidal transit sequence was introduced into the rice genome (C line). The transgenic lines, C4 and C5, were compared with the transgenic lines expressing TALA-S gene with plastidal transit sequence (P line) to investigate whether the plastidal sequence affects the targeting capacity of B. japonicum ALA-S gene and the ALA-synthesizing capacity in rice plants. The B. japonicum ALA-S mRNA was expressed efficiently in C lines and the protein was localized in the stroma of chloroplasts regardless of the transit sequence as in P lines. The resulting transgenic plants, C line, had similar levels of ALA-S activity, ALA, protoporphyrin IX and chlorophylls, compared to those of P lines. In response to irradiance of 350 μmol m^-2 s^-1, transgenic lines C4 and C5 displayed the characteristic phenotypes of photodynamic damage, i.e., decreases in photosynthetic parameter F_v/F_m, as in P5 and P14 lines, whereas wild type did not. These results indicate that the lack of the plastidal transit sequence influences neither chloroplast translocation of B. japonicum ALA-S nor ALA-synthesizing capacity in the transgenic rice.

Keywords: chlorophyll; chlorophyll a fluorescence; chloroplast translocation; porphyrin

Subjects: δ-aminolevulinic acid synthase; Bradyrhizobium japonicum; chlorophyll a,b; chlorophyll fluorescence; chloroplast; Oryza sativa; porphyrin; rice; transgenic plants

Received: March 1, 2008; Accepted: January 15, 2009; Published: June 1, 2010  Show citation