PLANT PHYSIOLOGY , Vol 106, Issue 1 37-43, Copyright © 1994 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
An Auxin-Inducible Element in Soybean SAUR Promoters
Y. Li, Z. B. Liu, X. Shi, G. Hagen and T. J. Guilfoyle
Department of Biochemistry, 117 Schweitzer, University of Missouri, Columbia, Missouri 65211
The soybean SAUR (Small Auxin-Up RNA) genes are transcriptionally induced
by exogenous auxins within a few minutes after hormone application. This
response is specifically induced by auxins primarily in epidermal and
cortical cells within elongation zones of hypocotyls and epicotyls. We have
previously shown that an 832-bp soybean SAUR promoter/[beta]-glucuronidase
(GUS) reporter gene fusion is responsive to auxin in transgenic tobacco
plants (Y. Li, G. Hagen, T.J. Guilfoyle [1991] Plant Cell 3: 1167-1175).
Similar results were obtained with an 868-bp SAUR 15A promoter-GUS reporter
gene in transgenic tobacco (Y. Li, unpublished results). We have now
analyzed a soybean SAUR 15A promoter in transgenic tobacco plants using
5[prime] unidirectional deletions, internal deletions and mutations, and
gain-of-function assays with a minimal cauliflower mosaic virus 35S
promoter. Our results indicate that the distal upstream element/Ndel
restriction endonuclease site element (NDE) (B.A. McClure, G. Hagen, C.S.
Brown, M.A. Gee, T.J. Guilfoyle [1989] Plant Cell 1: 229-239) in the SAUR
15A promoter is necessary and sufficient for auxin induction. Our results
also show that the 30-bp NDE portion of this element is responsible for
most, if not all, of the auxin inducibility of the SAUR 15A promoter. The
NDE contains two adjacent sequences, TGTCTC and GGTCCCAT, which have been
previously identified as putative auxin-responsive elements. We propose
that these elements might function independently or together, possibly with
an additional element(s), to confer auxin inducibility to the SAUR
promoters.