Abstract
In dicots, the key developmental process by which immature plastids differentiate into photosynthetically competent chloroplasts commences in the shoot apical meristem (SAM), within the shoot apex. Using laser-capture microdissection and single-cell RNA sequencing methodology, we studied the changes in the transcriptome along the chloroplast developmental pathway in the shoot apex of tomato seedlings. The analysis revealed the presence of transcripts for different chloroplast functions already in the stem cell-containing region of the SAM. Thereafter, an en masse up-regulation of genes encoding for various proteins occurs, including chloroplast ribosomal proteins and proteins involved in photosynthesis, photoprotection and detoxification of reactive oxygen species. The results highlight transcriptional events that operate during chloroplast biogenesis, leading to the rapid establishment of photosynthetic competence.
Highlights
The light-dependent reactions of oxygenic photosynthesis are carried out within extensive networks of flattened vesicles, called thylakoids
In dicots, which constitute the largest group of flowering plants, the aforementioned processes are initiated in the shoot apical meristem (SAM) and flanking leaf primordia (LP), collectively termed the ‘shoot apex’ (Fig. 1a)
The pattern of chlorophyll fluorescence in tomato generally resembles that of Arabidopsis[13], with no fluorescence apparent in the central area of the SAM below the L1 layer, and a sharp increase of fluorescence when moving from the central zone (CZ) to the peripheral zone (PZ), and to the LP (Fig. 1b)
Summary
Given the small size of the vegetative Arabidopsis SAM (diameter of 50–60 μm), we analyzed the relatively larger SAM of tomato, measuring 150–200 μm in diameter. It was found that genes that were upregulated along the developmental gradient were mostly related to protein translation, tetrapyrrole and carotenoid biosynthesis, plastid targeting, photosynthesis, Calvin cycle, redox regulation, very similar to the upregulated DEGs identified in our study (Fig. 6). The transcriptome analysis performed here revealed that expression of nuclear genes encoding chloroplast-targeted proteins occurs already in proplastid-containing stem cells of the SAM’s CZ, and increases in cells of the PZ and the LP In this respect, the transition from cell proliferation to cell expansion, highlighted in a previous study[28] as a key stage in which photosynthetic genes are strongly up-regulated, represents only the continuation of a gene expression gradient that is already established in the SAM. This is albeit the fact that the developmental gradient encompasses cells belonging to
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
