DISCOVERING THE SECRETS BEHIND THE GREENING STRATEGY IN

RAMÍREZ, LEONOR; VERGARA, ALEXANDER; VUORIJOKI, LINDA; STRAND, ÅSA

Umeå

Congreso; The 16th Nordic Photosynthesis Congress & The 5th Nordic Algae Symposium; 2023

Gymnosperms are able to partially green in darkness, contrary to what was established in Angiosperms, particularly in Arabidopsis thaliana, in which light is a determining factor for the onset of greening. These different strategies led us to study the molecular bases of the mechanisms that regulate greening in these plant lines. Previously, in our group was shown that the establishment of photosynthesis in Arabidopsis involves two distinct phases, the first phase is activated by light and induces rapid changes in gene expression, while the second phase depends on a retrograde signal originated in the plastid and generates massive changes in the expression of photosynthesis-associated nuclear genes (PhANGs) required for the development of fully functional chloroplasts. Our research group also contributed to the identification of GENOMES UNCOUPLED (GUN) 1 as the retrograde signal which suppresses greening in dark-grown Arabidopsis seedlings, repressing the transcriptional network controlling chloroplast development. In the current work, we hypothesized that the suppressive action from the GUN1 retrograde signal, essential for chloroplast development in angiosperms, is absent in gymnosperms leading to the partial greening in the dark. Our preliminary results suggest that first phase of greening occurs already in the dark in Norway Spruce. Regarding the second phase, we mathematically demonstrated that nuclear and plastid genomes in Norway Spruce are not connected via positive feedback as previously showed in Arabidopsis. In addition, we experimentally proved it by manipulating the greening process using lincomycin, a plastid protein translation inhibitor. Currently, we are studying the GUN1 function in Norway Spruce to link it to the different greening strategy compared to Arabidopsis. Understanding the regulatory mechanisms behind the greening process in Norway Spruce could help us understand how GUN1 and the retrograde signal are also controlled during the greening process in Arabidopsis.