Low frequency paternal transmission of plastid genes in Brassicaceae.

Plastid-encoded genes are maternally inherited in most plant species. Transgenes located on the plastid genome are thus within a natural confinement system, preventing their distribution via pollen. However, a low-frequency leakage of plastids via pollen seems to be universal in plants. Here we report that a very low-level paternal inheritance in Arabidopsis thaliana occurs under field conditions. As pollen donor an Arabidopsis accession (Ler-Ely) was used, which carried a plastid-localized atrazine resistance due to a point mutation in the psbA gene. The frequency of pollen transmission into F1 plants, based on their ability to express the atrazine resistance was 1.9 × 10(-5). We extended our analysis to another cruciferous species, the world-wide cultivated crop Brassica napus. First, we isolated a fertile and stable plastid transformant (T36) in a commercial cultivar of B. napus (cv Drakkar). In T36 the aadA and the bar genes were integrated in the inverted repeat region of the B. napus plastid DNA following particle bombardment of hypocotyl segments. Southern blot analysis confirmed transgene integration and homoplasmy of plastid DNA. Line T36 expressed Basta resistance from the inserted bar gene and this trait was used to estimate the frequency of pollen transmission into F1 plants. A frequency of <2.6 × 10(-5) was determined in the greenhouse. Taken together, our data show a very low rate of paternal plastid transmission in Brassicacea. Moreover, the establishment of plastid transformation in B. napus facilitates a safe use of this important crop plant for plant biotechnology.

The Arabidopsis Tellurite resistance C protein together with ALB3 is involved in photosystem II protein synthesis.

Assembly of photosystem II (PSII) occurs sequentially and requires several auxiliary proteins, such as ALB3 (ALBINO3). Here, we describe the role of the Arabidopsis thaliana thylakoid membrane protein Tellurite resistance C (AtTerC) in this process. Knockout of AtTerC was previously shown to be seedling-lethal. This phenotype was rescued by expressing TerC fused C-terminally to GFP in the terc-1 background, and the resulting terc-1TerC- GFP line and an artificial miRNA-based knockdown allele (amiR-TerC) were used to analyze the TerC function. The alterations in chlorophyll fluorescence and thylakoid ultrastructure observed in amiR-TerC plants and terc-1TerC- GFP were attributed to defects in PSII. We show that this phenotype resulted from a reduction in the rate of de novo synthesis of PSII core proteins, but later steps in PSII biogenesis appeared to be less affected. Yeast two-hybrid assays showed that TerC interacts with PSII proteins. In particular, its interaction with the PSII assembly factor ALB3 has been demonstrated by co-immunoprecipitation. ALB3 is thought to assist in incorporation of CP43 into PSII via interaction with Low PSII Accumulation2 (LPA2) Low PSII Accumulation3 (LPA3). Homozygous lpa2 mutants expressing amiR-TerC displayed markedly exacerbated phenotypes, leading to seedling lethality, indicating an additive effect. We propose a model in which TerC, together with ALB3, facilitates de novo synthesis of thylakoid membrane proteins, for instance CP43, at the membrane insertion step.