Studies on biosynthesis and functions of endogenous auxins in plants with distinct transport characteristics

Abstract

Auxin is the first discovered plant hormone that plays various physiological roles in plants.　Indole-3-acetic acid （IAA） is the most studied naturally occurring auxin and its action mechanism has been extensively investigated.　Recently, the main IAA biosynthetic pathway in plants has been settled by genetic and biochemical approaches.　IAA is mainly produced from tryptophan through the indole-3-pyruvate pathway in plants.　Phenylacetic acid （PAA） is another naturally occurring auxin of which physiological roles still remain unknown.　More recently, we demonstrated that PAA functions as auxin through the TIR1/AFB pathway, but it does not possess polar transport characteristics in plants unlike IAA.　These facts suggest that two types of auxins with distinct transport characteristics may cooperatively regulate plant growth and development, thus providing new insights into auxin biology.