Carbon monoxide improves adaptation of Arabidopsis to iron deficiency

Carbon monoxide (CO) is an endogenous gaseous molecule and regulates a variety of biological processes in animals. However, whether CO regulates nutrient stress responses in plants is largely unknown. In this paper, we described an observation that CO can regulate iron-homeostasis in iron-starved Arabidopsis. Exogenous CO at 50 microm was able to prevent the iron deficient-induced chlorosis and improve chlorophyll accumulation. Expression of AtIRT1, AtFRO2, AtFIT1 and AtFER1 was up-regulated by CO exposure in iron-deficient seedlings. CO-regulated iron homeostasis could also be found in monocot maize and green alga Chlamydomonas reinhardtii. Treatment with external CO increased iron accumulation in iron-deficient Arabidopsis and C. reinhardtii, and restored leaf greening in Maize ys1 and ys3 mutants (defective in Fe uptake). Moreover, endogenous CO level was increased in Arabidopsis under iron-deficiency. Finally, CO exposure induced NO accumulation in root tips. However, such an action could be blocked by NO scavenger cPTIO. These results indicate that CO may play an important role in improving plant adaptation to iron deficiency or cross-talking with NO under the iron deficiency.