INDUCTION OF A PROTEINASE-INHIBITOR II-CLASS GENE BY AUXIN IN TOMATO ROOTS

A cDNA clone corresponding to a transcript that was induced by auxin i n tomato seedling roots encodes a 223 amino acid protein belonging to the proteinase inhibitor II family of tomato and potato. The TR8 open reading frame has an N-terminal region with characteristics of a signa l peptide and three copies of a 64 amino acid segment that is also pre sent in multiple copies in other PI-II family members. Comparison to o ther serine proteinase inhibitors indicates that all three domains are trypsin-specific. Transcripts homologous to TR8 increased in abundanc e within 24 h of auxin treatment and continued to increase through 72 h, at which point the induction was approximately ten-fold. Auxin indu ction was observed in roots and hypocotyls, but not in cotyledons or e picotyls. Induction may therefore be correlated with lateral and adven titious root initiation, which occurs over a similar time frame in the same tissues. RFLPs detected with the TR8 probe were mapped to the lo ng arm of chromosome 11.