Regulation of tomato lateral root development by carbon monoxide and involvement in auxin and nitric oxide

Carbon monoxide (CO) is an endogenous gaseous molecule in organisms. Despite its reputation as a lethal gas, recent studies have shown that it is one of the most essential cellular components regulating a variety of biological processes. However, whether CO regulates physiological processes of morphological or developmental patterns in plants is largely unknown. In this paper, the observation that exogenous CO was able to promote the formation of tomato lateral roots (LR) is described. The CO stimulation of LR development was supported by analysis of tomato haem oxygenase-1 (LeHO-1), an enzymatic source of intracellular CO. It is shown that the amount of LeHO-1 proteins and transcripts increased parallel to the LR development. In addition, LeHO-1 loss-of-function tomato mutant yg-2 showed a phenotype of impaired LR development. The phenotype of yg-2 could be restored by treatment with CO. Since auxin is required for LR initiation and NO is shown to be a mediator for LR development, the correlation of CO with auxin and NO was tested. Our analysis revealed that the action of CO was blocked by the auxin transport inhibitor N-1-naphthylphthalamic acid and the NO scavenger cPTIO, respectively. Furthermore, the whole seedling assays of IAA show that treatment with CO increased the overall IAA levels in various tissues of tomato. Exposure of tomato roots to CO also enhanced intracellular NO generation. These results indicate that CO plays a critical role in controlling architectural change in tomato roots.