Stress responses in alfalfa (Medicago sativa L.) 12. Sequence analysis of phenylalanine ammonia-lyase (PAL) cDNA clones and appearance of PAL transcripts in elicitor-treated cell cultures and developing plants

Abstract

An expression library containing cDNAs derived from transcripts from fungal elicitor-treated alfalfa cell suspension cultures was screened with an antiserum raised against phenylalanine ammonia-lyase (PAL) from alfalfa. A single immunoreactive clone was isolated which encoded a full-length PAL cDNA (APAL1) consisting of a 2175 bp open reading frame, 96 bp 5'-untranslated leader and 128 bp 3'-non-coding region. The deduced amino acid sequence was 86.5% similar to that of the PAL2 gene of bean, and encoded a polypeptide of Mr 78,865. A second PAL cDNA species was isolated, whose 3'-untranslated region was 86% identical to that of APAL1. Southern blot analysis indicated that PAL is encoded by a small multigene family in alfalfa. PAL transcript levels were rapidly and massively induced, and preceded increased PAL extractable activity, on exposure of alfalfa suspension cells to elicitor from baker's yeast. PAL transcripts were most abundant in roots, stems and petioles during growth and development of alfalfa seedlings. These studies provide the basis for an examination of the developmental and environmental control of a key enzyme of phenylpropanoid synthesis in a plant species which is readily amenable to stable genetic transformation.