Ecotype-specific responses to HLC growth for photosynthesis
While both IT and SW exhibited strong photosynthetic upregulation and transcriptomic differential regulation in HLC (with ~6.5% of total leaf transcriptome induced and ~6.1% downregulated relative to LLW), the marked ecotype-specific difference between two ecotypes under HLC in the expression of genes related to photosynthesis is consistent with the greater upregulation of photosynthesis in SW compared to IT in response to both high light and low temperature (Adams et al., 2014, 2016, 2018; Cohu et al., 2013b; Stewart et al., 2015, 2016, 2017). Genes activated in SW under HLC included genes involved in carbon assimilation and aspects of photoprotective energy dissipation via antioxidants and cyclic electron flow around PSI. These gene expression responses mirrored the higher photosynthetic capacity, higher chlorophyll a+ b per unit area and more oxidized QA reduction state of SW versus IT in HLC. In contrast, the downregulation of genes involved in light harvesting in IT under HLC suggest that IT avoids excess light by reducing light-collection capacity rather than solely upregulating photosynthesis and photoprotective energy dissipation as seen in SW. These transcriptomic findings are consistent with the more highly reduced QA state, lower chlorophyll a +b per unit per area, and higher chlorophyll a/b ratio (indicative of preferential degradation of the outer, chlorophyllb -containing light-harvesting complexes) in IT versus SW under HLC.