Role of salicylic acid in low CO2response in Arabidopsis

Abstract

Plants use CO2to produce carbohydrates via photosynthesis. A number of studies have focused on the high CO2response of plants, whereas little is known about the low CO2response of plants. Considering that phytohormones regulate responses to various environmental stresses, we hypothesized that they might also regulate the low CO2response. In this study, we show that Arabidopsis plants adjust the low CO2response by inducing salicylic acid (SA) and abscisic acid (ABA). Phytohormone analysis revealed a dramatic increase in SA under low CO2conditions. Furthermore, the increase in SA was completely abolished in salicylic acid induction-deficient2mutant, indicating that SA is primarily synthesized via isochorismate synthase under low CO2conditions. The level of ABA also increased under low CO2conditions. Consistent with these observations, the expression of genes involved in SA and ABA accumulation was altered in response to low CO2concentrations. Gene expression analysis indicated that the expression of SA- and ABA-responsive genes increased under low CO2conditions, although SA response of Pathogenesis-Relatedgenes was compromised. Under low CO2conditions, it became evident that the expression of programmed cell death-associated genes was altered, and that of photosynthesis-associated genes was suppressed. The responses of these genes were further manifested when plants accumulated high levels of SA. Taken together, we suggest that plants increase their levels of SA and ABA in response to low CO2environments. Furthermore, the increase in SA appears to be associated with the suppression of non-essential genes and the alteration of cell death-associated genes.

Keywords: Arabidopsis; abscisic acid; gene expression; low CO2; salicylic acid.