Soluble Cell Wall Compounds from Carrot Roots Induce the picA and pgl Loci of Agrobacterium tumefaciens. Lijun Rong. Department of Biological Sciences, Purdue University, West Lafayette, IN 47907. Nicholas C. Carplta(2), Andrew Mort(3), and Stanton B. Gelvin(1). (1) Department of Biological Sciences and (2) Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907, and (3) department of Biochemistry, Oklahoma State University, Stillwater 74078 U.S.A. MPMI 7:6-14. Accepted 8 October 1993. Copyright 1994 The American Phytopathological Society.

Crude extracts from carrot roots induce the picA chromosomal locus of Agrobacterium tumefaciens. The inducer is a complex pectic polysaccharide whose activity can be destroyed by incubation with a highly purified cloned pectate lyase (PelE protein of Erwinia chrysanthemi EC16). Oligogalacturonates of degree of polymerization (dp) 6-17 induce the picA locus, with peak activity at dp 8. However, the inducing compound partially purified from carrot root extracts is about 100-fold more active (per uronic acid content) than is the most active oligogalacturonate in inducing the picA locus. Chemical linkage analysis of a QAE Sephadex fraction containing peak inducing activity from the carrot extract indicates that it contains a complex mixture of acidic and neutral sugars. The inducer is not simply a rhamnogalacturonan hut requires both arab-inose and galacturonic acid for activity. De-esterification by alkali treatment of the carrot inducer also increases activity. Partially purified inducing compound from carrot root extracts can induce the pic A locus at galacturo-nate concentrations of 5-10 (M, suggesting that it may act as a signal molecule from the plant. Compounds from carrot root extracts also induce the pgl locus, which encodes a predicted protein with homology to known polygalacturonases.