Transgenic Tomato Plants with a Modified Ability to Synthesize Indole-3-acetyl-β-1-O-D -glucose
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Esterification of indole-3-acetic acid (IAA) is thought to be an important component in the homeostatic regulation of the levels of this phytohormone. To better understand the role of the initial step in IAA esterification in the control of IAA levels, transgenic tomato plants were generated that either express maize IAGLU or have reduced levels of the enzyme IAA-glucose synthetase. These plants were obtained by expressing maize IAGLU in either sense or antisense orientation using the CaMV35S promoter. The maize IAGLU probe hybridized to two transcripts (1.3 kb and 2.5 kb) in wild-type tomato vegetative tissue and green fruit. The sense and antisense transformants exhibited distinct phenotypic characteristics. Sense transformants showed an almost complete lack of root initiation and development. Antisense transgenic plants, on the other hand, had unusually well developed root systems at early stages in development, and the amount of the endogenous 75 kDa IAGLU protein was reduced. IAGLU antisense plants also had reduced levels of IAA-glucose and lower esterified IAA.
KeywordsAuxin conjugation Glucosyltransferase Indoleacetyl-glucose Lycopersicon esculentum Phytohormone Transgenic tomato
We thank Dr. Robert S. Bandurski, Michigan State University, for providing maize IAGLU and authorizing its use in our studies, and for helpful advice during the early stages of this work. We also thank Dr. Harry J. Swartz (University of Maryland, College Park) for his help with tomato grafting and Dr. M. Kowalczyk (Umeå, Sweden) for the gift of the two IAGLU antibodies. We thank Drs. Jennifer Normanly (University of Massachusetts) and Jutta Ludwig-Müller (TU-Universität, Dresden, Germany) for their critical reading of the manuscript and helpful comments. This paper is dedicated to the memory of our friend and colleague, Dr. Jedrzej B. Szerszen, who cloned maize IAGLU, thus making the current work possible. This research was supported by U.S.–Israel Binational Research and Development (BARD) Fund grant US-2498-94, U.S. Department of Energy grant DE-FG02-00ER15079, and U.S. National Science Foundation grant IBN 0111530.
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