IAA synthesis and root induction with iaa genes under heat shock promoter control

Abstract

We have devised a heat shock-inducible indole-3-acetic acid (IAA) synthesis system for plant cells, which is based on the iaa genes of the Agrobacterium tumefaciens T-DNA and the heat shock promoter hsp70 of Drosophila melanogaster. Two DNA constructs were tested: one contains the iaaM gene linked to the hsp70 promoter (hsp70-iaaM) and encodes the production of indoleacetamide (IAM), the other contains hsp70-iaaM and the wild-type iaaH gene which codes for the conversion of IAM into IAA (hsp70-iaaM/iaaH). Heat shock-controlled IAM and IAA synthesis was tested on two levels: biochemically by measuring IAM and IAA levels in Kalanchoe stem segments infected with the two constructs, and morphologically by IAA-dependent root formation on Kalanchoe plants, on carrot discs and on tobacco leaf fragments. At both levels the responses were found to be controlled by the heat shock promoter. IAM levels of segments infected with hsp70-iaaM increased 6-fold upon heat shock induction to 240 pmol IAM per stem segment. The accumulation of IAA in segments infected with hsp70-iaaM/iaaH and heat-shocked was found to be more variable, possibly due to IAA transport and metabolism. Heat shock treatment of Kalanchoe plants and tobacco leaf fragments infected with hsp70-iaaM/iaaH led to a strong increase in root formation. On carrot discs, heat shock-specific root induction was also demonstrated, but the responses differed between individual carrots.

Analysis of lateral root growth in Arabidopsis in response to physiologically active auxin analogues

“…It is known that the number of LR can be altered by the application of auxin or by the perturbation of internal auxin levels (Blakely et al, 1982;Kares et al, 1990). Auxin transported from the shoot is necessary for LR formation in young seedlings (Casimiro et al, 2001).…”

Differential activation of the primary auxin response genes, PS‐IAA4/5 and PS‐IAA6, during early plant development

“…CycIAt expression is restricted to the lateral root primordium and, later in development, to the meristematic zone in a cell-specific pattern similar to that observed in the primary root (Ferreira et aL, 1994). Cell cycle progression is under hormonal control (Jacobs, 1995), and several lines of evidence suggest that auxin is intricately involved in lateral root initiation and development: (i), exogenous application of auxin initiates lateral roots in a wide variety of plants (Kerk, 1990;Thimann, 1936;Torrey, 1950); (ii), transgene-mediated overexpression of auxin results in plants with increased lateral root production (Kares et aL, 1990;Klee et aL, 1987); (iii) auxin-insensitive mutants of tomato, dgt (Kelly and Bradford, 1986), and Arabidopsis, auxl, axrl, axr4 (Hobble and Estelle, 1995), are defective in lateral root formation; and (iv) a mutant impaired in lateral root maturation, alf3-1, can be rescued by IAA (Celenza et aL, 1995).…”

Nitric oxide mediates strigolactone signaling in auxin and ethylene-sensitive lateral root formation in sunflower seedlings

“…Exogenous application of IAA induces lateral root formation and increases the production of lateral roots in transgenic plants which overexpress bacterial IAA biosynthetic genes, suggesting the role of IAA as a signal molecule in lateral root initiation in plant. [18][19][20][21] Auxin-signaling plays an important role in pericycle priming, initiation of cell division, and LRP formation to LR emergence. 22 Recent work in Arabidopsis thaliana mutant has suggested the role of IAA in the initiation of cell division in the pericycle and promotion of cell division and maintenance of cell viability in the developing lateral root.…”