Modeling-based age-dependent analysis reveals the net patterns of ethylene-dependent and -independent aerenchyma formation in rice and maize roots.

Plants require oxygen for the functioning of roots, and thus the establishment of a long-distance diffusion path from above-water tissues to the submerged roots is essential to survive flooding. Rice (Oryza sativa) constitutively forms aerenchyma (gas spaces) under aerobic conditions, and induces its formation in response to low-oxygen conditions. Constitutive aerenchyma formation in rice roots is regulated by the phytohormone auxin, whereas ethylene stimulates inducible aerenchyma formation. However, the net patterns of the ethylene-dependent and -independent (auxin-dependent) aerenchyma formation remain unclear. In the present study, we used a modeling approach to determine age-dependent aerenchyma formation in the wild-type rice and reduced culm number 1 mutant, in which ethylene production is reduced, to reveal the net patterns of ethylene-dependent and -independent aerenchyma formation. Subsequent comparison of age-dependent aerenchyma formation between rice and maize roots suggested that more rapid induction of ethylene-dependent aerenchyma formation and more aerenchyma in rice roots are essential to achieve efficient oxygen diffusion under low-oxygen conditions. Moreover, rice roots showed rapid increase in the expression levels of ethylene biosynthesis and responsive genes, suggesting that the local ethylene production at an early time point after root-cell emergence contributes to the rapid induction of the ethylene-dependent aerenchyma formation in rice. DATA AVAILABILITY: All data included in this study are available upon request by contact with the corresponding author.