CHARACTERIZATION OF 2 PROTEINASE-INHIBITOR (ATI) CDNAS FROM ALFALFA LEAVES (MEDICAGO-SATIVA VAR VERNEMA) - THE EXPRESSION OF ATI GENES IN RESPONSE TO WOUNDING AND SOIL-MICROORGANISMS

cDNAs encoding two Bowman-Birk proteinase inhibitors were isolated fro m the leaves of alfalfa (Medicago sativa). The cDNAs are derived from a small gene family (3 to 10 genes) encoding alfalfa trypsin inhibitor s (ATIs). Each cDNA clone encoded a mature ATI that was part of a larg er, putative preprotein. ATI mRNAs are continuously expressed in flowe r parts, but are mechanically wound-inducible in the stems and leaves. ATI mRNA is shown to be continuously present in roots of soil-grown p lants, but its presence is primarily in response to microorganisms pre sent in the soil. Additionally, while mechanical wounding of the alfal fa roots induced ATI mRNA synthesis both in the roots and in the leave s, microbial infection of the roots triggered ATI mRNA synthesis in th e roots but not in the leaves. These results suggest that both local a nd systemic signalling pathways for proteinase inhibitor synthesis are present in alfalfa plants.