BEAN CLASS-IV CHITINASE GENE - STRUCTURE, DEVELOPMENTAL EXPRESSION AND INDUCTION BY HEAT-STRESS

A P4-chitinase genomic sequence was isolated from a bean (Phaseolus vu lgaris) genomic library using a P4-ch cDNA. The complete sequence of t he P4-ch gene was determined. Primer extension analysis allowed the id entification of the transcriptional start site located 79 bp upstream of the translational initiation codon. The gene is interrupted by an i ntervening sequence. In the 5' upstream region, a TATT box occurs in p lace of a TATA at position -33, while a typical CAAT box is found at p osition -73 with respect to the transcription initiation site. Gibbere llic acid, heat shock and salicylic acid regulatory responsive sequenc es were also identified. Transient expression of chimeric genes in tob acco protoplasts indicated that all the elements required for expressi on of the coding sequences are present within the first 600 bp of P4-c h 5' flanking DNA. Various stress conditions such as wounding, salicyl ic acid and NaCl treatments, heat and cold stress have been applied to the plants. Whereas wounding, NaCl treatment and cold stress are inef fective, transcription of P4-mRNAs is induced upon salicylic acid trea tment and, surprisingly, in response to heat stress. P4-chitinase is i nduced during germination and seems to be constitutively expressed in roots of mature plants.