CHARACTERIZATION OF LEMIR, A ROOT-KNOT NEMATODE-INDUCED GENE IN TOMATO WITH AN ENCODED PRODUCT SECRETED FROM THE ROOT

A tomato gene that is induced early after infection of tomato (Lycoper sicon esculentum Mill.) with root-knot nematodes (Meloidogyne javanica ) encodes a protein with 54% amino acid identity to miraculin, a flavo rless protein that causes sour substances to be perceived as sweet. Th is gene was therefore named LeMir (L. esculentum miraculin). Sequence similarity places the encoded protein in the soybean trypsin-inhibitor family (Kunitz). LeMir mRNA is found in root, hypocotyl, and flower t issues, with the highest expression in the root. Rapid induction of ex pression upon nematode infection is localized to root tips. In situ hy bridization shows that LeMir is expressed constitutively in the root-c ap and root-tip epidermis. The LeMir protein product (LeMir) was produ ced in the yeast Pichia pastoris for generation of antibodies. Western -blot analysis showed that LeMir expression is up-regulated by nematod e infection and by wounding. LeMir is also expressed in tomato callus tissue. Immunoprint analysis revealed that LeMir is expressed througho ut the seedling root, but that levels are highest at the root/shoot ju nction. Analysis of seedling root exudates revealed that LeMir is secr eted from the root into the surrounding environment, suggesting that i t may interact with soil-borne microorganisms.