Functional identification of a trehalose 6-phosphate phosphatase gene that is involved in transient induction of trehalose biosynthesis during chilling stress in rice

Trehalose serves as a stress protectant and/or reserve carbohydrate in a variety of organisms including bacteria, yeast, and invertebrates. Recently, trace amounts of trehalose have been detected in higher plants, although the function of trehalose in plants remains unknown. A cDNA clone (OsTPP1) encoding a putative trehalose-6-phosphate phosphatase (TPP) for trehalose biosynthesis was isolated from rice. Functionality of the clone was demonstrated by complementation of a yeast mutant and enzymatic activity of the recombinant protein. Northern blots revealed that the OsTPP1 transcript levels were fairly low or under detectable limits in most of the tissues under ambient conditions but were highly induced within 1-2 h of chilling stress (12 degrees C) in both root and shoot tissues of seedlings. This induction was transient and disappeared after 6 h of the chilling stress. Transient expression of OsTPP1 was also induced under severe chilling stress (4 degrees C) as well as salinity and drought stresses at ambient temperatures. Application of exogenous ABA (50 mu M) resulted in a transient increase of OsTPP1 expression within 20 min of the treatment, thereby suggesting involvement of ABA in OsTPP1 gene regulation. Measurements of total cellular TPP activity and trehalose content in roots indicated that both TPP activity and trehalose levels were transiently increased after chilling (12 degrees C) stress. Collectively, the data indicate that transient activation of trehalose biosynthesis is involved in early chilling stress response in rice. Possible functions of trehalose in the early stages of chilling stress response are discussed.