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.