A Class II small heat shock protein OsHsp18.0 plays positive roles in both biotic and abiotic defense responses in rice.

Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most devastating diseases of rice. However, the molecular mechanism underpinning the Xoo resistance of rice is still not fully understood. Here, we report that a class II small heat shock protein gene, OsHsp18.0, whose expression was differentially induced between a resistant and a susceptible variety in response to Xoo infection, plays positive roles in both biotic and abiotic resistance. The molecular chaperone activity of OsHsp18.0 was confirmed by a bacterium-expressed glutathione S-transferase fusion protein. Overexpression of OsHsp18.0 in a susceptible rice variety significantly enhanced its resistance to multiple Xoo strains, whereas silencing of OsHsp18.0 in a resistant variety drastically increased its susceptibility. The enhanced Xoo resistance in OsHsp18.0-overexpressing lines was positively correlated with the sensitized salicylic acid-dependent defense responses. In addition to disease resistance, the OsHsp18.0 overexpressing and silencing lines exhibited enhanced and reduced tolerance, respectively, to heat and salt treatments. The subcellular localization study revealed that the green fluorescent protein-OsHsp18.0 was enriched on the nuclear envelope, suggesting a potential role of OsHsp18.0 in the nucleo-cytoplasmic trafficking. Together, our results reveal that the rice OsHsp18.0 is a positive regulator in both biotic and abiotic defense responses.