A GH3 family member, OsGH3-2, modulates auxin and abscisic acid levels and differentially affects drought and cold tolerance in rice

Plant responses to abiotic stresses are coordinated by arrays of growth and developmental processes. Indole-3-acetic acid (IAA) and abscisic acid (ABA) play critical roles in developmental programmes and environmental responses, respectively, through complex signalling and metabolism networks. However, crosstalk between the two phytohormones in the stress responses remains largely unknown. Here, it is reported that a GH3 family gene, OsGH3-2, encoding an enzyme catalysing IAA conjugation to amino acids, is involved in the modulation of ABA level and stress tolerance. Expression of OsGH3-2 was induced by drought but was suppressed by cold. Overexpression of OsGH3-2 in rice caused significant morphological aberrations related to IAA deficiency, such as dwarfism, smaller leaves, and fewer crown roots and root hairs. The overexpressing line showed significantly reduced carotene, ABA, and free IAA levels, greater stomata aperture, and faster water loss, and was hypersensitive to drought stress. However, the overexpressing line showed increased cold tolerance, which was due to the combined effects of reduced free IAA content, alleviated oxidative damage, and decreased membrane penetrability. Furthermore, expression levels of some ABA synthesis- and stress-related genes were significantly changed in the overexpression line. It was conclude that OsGH3-2 modulates both endogenous free IAA and ABA homeostasis and differentially affects drought and cold tolerance in rice.