Plants constantly monitor their environment and adjust the allocation of their resources: they stimulate growth or, on the contrary, slow it down to better adapt to extreme weather conditions or defend against microbial aggressions. This balance is regulated by networks of hormones that act synergistically or antagonistically to deploy the best response and promote survival.
The antagonism between the formation of jasmonate-type hormones (JAs) and vegetative growth has long been known. Jasmonic acid (JA) is rapidly produced in leaves attacked by insect herbivores or infection, and acquires its hormonal activity through the formation of the JA-Ile conjugate, to trigger the synthesis of a multitude of defense compounds, while slowing down photosynthesis and growth. Alternatively, JA can be oxidized by enzymes called Jasmonic Acid Oxidases (JAO) towards hydroxy-JA (OH-JA), an inactive intermediate leading to presumed storage forms.
In a study published on April 24 2025 in Plant Physiology, Thierry Heitz and his colleagues from Emmanuel Gaquerel’s team at IBMP show, in a collaboration between 4 laboratories in France and Germany, that these two metabolic fates of JA underlie an important mechanism for regulating the growth/defense balance in rice.
Using a model they previously discovered in the laboratory plant Arabidopsis thaliana, the researchers demonstrated the existence of a family of JA oxidizing enzymes in Rice, and discovered their conserved regulatory role in this cereal. By using CrisprCas9 to generate a series of lines deficient in one or more JAOgenes, they found that the growth of young mutant plants is retarded. Their molecular analysis identified a metabolic redirection towards JA-Ile and its derivatives at the expense of OH-JA, concomitant with increased basal accumulation of defense compounds. Inoculation with the blast agent showed increased resistance to this fungal disease in the mutants.
The results indicate that even in the absence of stress, metabolic management of trace amounts of the hormone precursor JA is crucial for adjusting the growth/defense balance in rice. They provide a new toolfor targeting traits of agronomic interest in this major cereal.
