BBX21 overexpression promotes photosynthesis in Arabidopsis. A, Photosynthesis, transpiration rate, stomatal conductance, and internal concentration of CO2 as function of PPFD (n = 4). B, WUE as function of PPFD (n = 4). C, FD1, RCA, and LHCA transcripts (n = 3). n = number of biological replicates. Mean values are shown with error bars indicating se. Data were analyzed by Student’s t tests, and asterisks indicate significant difference between Col and BBX21-OE plants (*P < 0.05 and **P < 0.01; NS, not significant).