No abstract

Owing to their sessile life habit, plants are continuously subjected to a broad range of environmental stresses. During periods of (a)biotic stresses, reactive oxygen species (ROS) levels can rise excessively, leading to oxidative stress. Glutathione reductase (GR) plays an important role in scavenging the ROS and maintenance of redox potential of the cell during oxidative stress. To enhance ROS scavenging capacity, and hence stress tolerance, the Arabidopsis thalianaGR2 (AtGR2) gene was expressed from the tobacco plastid (chloroplast) genome, the main source of ROS production in plant photosynthetic tissues, in this study. Leaves of transplastomic tobacco plants had about seven times GR activity and 1.5 times total glutathione levels compared to wild type. These transplastomic tobacco plants showed no discernible phenotype and exhibited more tolerance to methyl viologen-induced oxidative stress than wild-type control plants. The results indicate that introducing AtGR2 in chloroplasts is an efficient approach to increase stress tolerance. This study also provides evidence that increasing antioxidant enzyme via plastid genome engineering is an alternative to enhance plant’s tolerance to stressful conditions.

Key messageGlobal survey of plastid transcriptional activities during fruit ripening in kiwifruit showed great changes in gene expression and provided cis-elements for engineering the plastid genome of kiwifruit in future.

A serious limitation in the application of plastid biotechnology is the low-level expression of transgene in non-green plastids like chromoplasts compared with photosynthetically active chloroplasts. Unlike other fruits, not all chloroplasts are transformed into chromoplast during ripening of red-fleshed kiwifruit ( Actinidia chinensis vs Hongyang) fruits, which may make kiwifruit as an ideal horticultural plant for oral vaccine production by plastid engineering. To identify cis -elements potentially triggering high-level transgene expression in edible tissues of the ‘Hongyang’ kiwifruit, here we report a comprehensive analysis of kiwifruit plastid gene transcription in the green leaves and fruits at three different developing stages. While transcripts of a few photosynthesis-related genes and most genetic system genes were substantially upregulated in green fruits compared with leaves, nearly all plastid genes were significantly downregulated at the RNA level during fruit development. Expression of a few genes remained unchanged, including psbA , the gene encoding the D1 polypeptide of photosystem II. However, PsbA protein accumulation decreased continuously during chloroplast-to-chromoplast differentiation. Analysis of post-transcriptional steps in mRNA maturation, including intron splicing and RNA editing, revealed that splicing and editing may contribute to regulating plastid gene expression. Altogether, 40 RNA editing sites were verified, and five of them were newly discovered. Taken together, this study has generated a valuable resource for the analysis of plastid gene expression, and provides cis -elements for future efforts to engineer the plastid genome of kiwifruit.