A novel subtilisin-like protease gene from Arabidopsis thaliana is expressed at sites of lateral root emergence.

Differential screening of a cDNA library for mRNA species that specifically accumulate during auxin-induced lateral root formation in Arabidopsis thaliana led to the isolation of the AIR3 cDNA clone. The corresponding single copy gene consists of 10 exons which encode a protein that possesses all the characteristics of subtilisin-like proteases. The promoter of the AIR3 gene was fused to the gusA (beta-glucuronidase) reporter gene and introduced into Arabidopsis. Expression was almost completely restricted to the outer layers of the parental root at sites of lateral root emergence and could be observed even before protrusion of the newly formed root tip. In the presence of external auxin, GUS activity was visible throughout the parts of the root that are competent for lateral root formation. By digesting structural proteins in the extracellular matrix of cells located above sites of lateral root formation, AIR3 might weaken cell-to-cell connections and thus facilitate lateral root emergence.