Why are conifers green in the dark?

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

Umeå

Simposio; INUPRAG Symposium on Integrative Plant Biology; 2023

One of the most dramatic challenges in the life of a plant occurs when the seedling emerges from the soil and exposure to light triggers the establishment of photosynthesis. In angiosperms such as Arabidopsis, this process is tightly regulated as premature accumulation of light harvesting proteins and photoreactive chlorophyll precursors cause oxidative damage when the seedling is first exposed to light. Chloroplasts communicate their developmental and physiological status to the nucleus via retrograde signaling, ensuring proper nuclear gene expression. Some gymnosperms conifer species such as Norway spruce (Picea abies) adopted a different strategy where dark germinated seedlings possess the ability to accumulate chloropyll and, more surprisingly, they can produce rather differentiated chloroplasts with grana. GENOMES UNCOUPLED1 (GUN1)-dependent retrograde signal regulates the expression of several key transcription factors during the critical step of seedling emergence from darkness in Arabidopsis. We have preliminary data suggesting that GUN1 has a different function in conifers. Currently, we are looking for the answer to several questions associated with understanding the establishment of functional chloroplasts in Spruce: i) What characteristics of the establishment of photosynthetically active chloroplasts are light dependent?, ii) Could the greening strategy observed in Spruce be explained by a different function of GUN1 relative to Arabidopsis?, iii) Which components of the greening strategy in Spruce show a key role from an evolutionary point of view? Through this project we will contribute to the knowledge of the regulatory mechanisms details behind the strategies employed by Spruce and Arabidopsis.