Temperature-induced lipocalins (TIL) have been shown to be responsive to heat stress in wheat and Arabidopsis, but the nature of this response was unknown.In this study, a reverse genetic approach was taken to elucidate the role of Arabidopsis TIL1 (At5g58070) in thermotolerance.A T-DNA knockout line of TIL1 (til1-1) showed severe defects in basal and acquired thermotolerance, which could be complemented by introducing the wild-type gene.However, over-expression of TIL1 did not significantly enhance thermotolerance in transgenic plants.TIL1 is peripherally associated with plasma membrane.