Gene expression under water deficit in loblolly pine (Pinus taeda): Isolation and characterization of cDNA clones

Poly(A(+)) RNA was extracted from roots of loblolly pine (Pinus taeda L.) seedlings subjected to gradual and prolonged water deficit. This RNA was used to construct a cDNA library. A number of cDNA clones were isolated whose expression was induced by water deficit. Four of these cDNA clones, designated pLP2, pLP3, pLP4 and pLP5, were characterized further. Each of these pine genes has unique characteristics either in sequence or pattern of expression, The protein encoded by pLP2 shows 91% identity to S-adenosylmethionine synthetase from a range of plants. The protein encoded by pLP3 is similar to a tomato protein induced by water deficit and during fruit ripening, but the pine protein possesses a unique 34-amino-acid region near the amino terminal. The LP4 protein is similar to stellacyanin, a copper-binding protein in the Japanese lacquer tree, but possesses a proline/serine-rich carboxy terminus not found in other plants. Clone pLP5 encodes a novel glycine-rich protein with similarity to both silk fibroin and the rat chondroitin core protein, but the putative pine protein is distinct from previously characterized glycine-rich proteins. Transcript levels of the four genes rose under moderate water deficit stress and then declined as stress became severe (1 month without water), with the exception of pLP5 mRNA, which remained at elevated levels even under severe stress. The possible roles of the encoded proteins in cell wall reinforcement are discussed.