The indoleacetic acid-lysine synthetase gene of Pseudomonas syringae subsp. savastanoi induces developmental alterations in transgenic tobacco and potato plants

Abstract

The iaaL gene of Pseudomonas syringae subsp. savastanoi encodes an indoleacetic acid-lysine synthetase that conjugates lysine to indoleacetic acid. A chimaeric gene consisting of the iaaL coding region under the control of the 35S RNA promoter from cauliflower mosaic virus (35SiaaL) has been used to test if iaaL gene expression leads to morphological alterations in tobacco and potato. Transgenic tobacco plantlets bearing this construct have been shown to synthesize IAA-[14C]lysine when fed with [14C]lysine. In late stages of development, their leaves show an increased nastic curvature (epinasty) of the petiole and midvein, a finding suggestive of an abnormal auxin metabolism. The alteration is transmitted to progeny as a dominant Mendelian trait cosegregating with the kanamycin resistance marker. Transgenic potato plants harbouring the construct are also characterized by petiole epinasty. Moreover, 35SiaaL transgenic plants have an increased internode length in potato and decreased root growth in both tobacco and potato. An increased content of IAA-conjugates in leaf blade was found to correlate with the epinastic alterations caused by iaaL gene expression in tobacco leaves. These data provide evidence that IAA conjugation is able to modulate hormone action, suggesting that the widespread endogenous auxin-conjugating activities are of physiological importance.

Superroot, a recessive mutation in Arabidopsis, confers auxin overproduction.

“…In transgenic tobacco plants producing an IAA-lysine synthetase, an increase in auxin conjugates was observed. This increase in the level of conjugates was not always correlated with a comparable decrease in the level of free IAA, indicating that de novo IAA biosynthesis is partially controlled by the level of conjugation (Romano et al, 1991;Spena et al, 1991). Although an increase in IAA conjugation is not necessarily correlated with a decrease in free IAA, significantly increased IAA levels have not been observed in these transgenic plants.…”

“…The expression of bacterial auxin biosynthesis genes in plants results in the overproduction of both indole-3-acetic acid (IAA) and IAA conjugates (Klee et al, 1987;Sitbon et al, 1991Sitbon et al, , 1992Sitbon et al, , 1993Romano et al, 1993). The expression of the bacterial IAAlysine synthetase gene leads to the accumulation of IAA conjugates in plants but not necessarily to a comparable decrease in the level of free IAA (Romano et al, 1991;Spena et al, 1991). These studies strongly suggest that the level of free IAA in the plant is controlled by both de novo biosynthesis and conjugation (reviewed by Hobbie and Estelle, 1994).…”

The Role of Auxin, pH, and Stress in the Activation of Embryogenic Cell Division in Leaf Protoplast-Derived Cells of Alfalfa

“…There is substantial evidence to support the hypothesis that not only free but also conjugated IAA might have biological activity (e.g. Spena et al, 1991). It is also obvious that the significant increase in the cellular level of conjugated IAA forms has to be preceded by the synthesis of free IAA.…”

Sur2 mutations of Arabidopsis thaliana define a new locus involved in the control of auxin homeostasis

“…The expression of bacterial auxin biosynthesis genes in plants results in the overproduction of both free and conjugated IAA forms (Klee et al, 1987;Romano et al, 1993;Sitbon et al, 1991Sitbon et al, , 1992Sitbon et al, , 1993. Alternatively, in transgenic tobacco plants producing an IAA-lysine synthetase, an increase in auxin conjugates was observed which was not always correlated with a comparable decrease in the level of free IAA (Romano et al, 1991;Spena et al, 1991). These studies strongly suggest that the level of free IAA in the plant is controlled by both de novo biosynthesis and conjugation (reviewed by Hobbie and Estelle, 1994).…”