Auxin-Regulated Gene Expression

A number of cDNA clones to independent mRNAs that increase in amount after brief exposure to auxins have been isolated. From soybean, sequenced, and characterized. Increases in mRNA abundance can be detected as early as 2.5 minutes after auxin application to excised elongating regions of soybean hypocotyls. Increased transcription rates on the genes which encode the auxin-responsive mRNAs account, at least partly, for the accumulation of mRNAs. A variety of auxins induce the accumulation of the mRNAs, but other plant hormones have no effect on the mRNA abundance. Some of the genes which encode the mRNAs are clustered in the soybean genome. The soybean gene cluster is expressed under auxin control when transferred into petunia via Agrobacterium T-DNA. In soybean and pea, expression of some of the auxin regulated genes is greatest in the elongating regions of hypocotyl and epicotyl. Some of the genes are primarily expressed in epidermal and outer cortical cells of elongating hypocotyl region. During gravitropism, some of the auxin responsive mRNAs turn over very rapidly and accumulate on the more rapidly elongating side of the hypocotyl