Auxin Signaling in Arabidopsis Leaf Vascular Development

Abstract

A number of observations have implicated auxin in the formation of vascular tissues in plant organs. These include vascular strand formation in response to local auxin application, the effects of impaired auxin transport on vascular patterns and suggestive phenotypes of Arabidopsis auxin response mutants. In this study, we have used molecular markers to visualize auxin response patterns in developing Arabidopsis leaves as well as Arabidopsis mutants and transgenic plants to trace pathways of auxin signal transduction controlling the expression of early procambial genes. We show that in young Arabidopsis leaf primordia, molecular auxin response patterns presage sites of procambial differentiation. This is the case not only in normal development but also upon experimental manipulation of auxin transport suggesting that local auxin signals are instrumental in patterning Arabidopsis leaf vasculature. We further found that the activity of the Arabidopsis gene MONOPTEROS, which is required for proper vascular differentiation, is also essential in a spectrum of auxin responses, which include the regulation of rapidly auxin-inducible AUX/IAA genes, and discovered the tissue-specific vascular expression profile of the class I homeodomain-leucine zipper gene, AtHB20. Interestingly, MONOPTEROSactivity is a limiting factor in the expression of AtHB8and AtHB20, two genes encoding transcriptional regulators expressed early in procambial development. Our observations connect general auxin signaling with early controls of vascular differentiation and suggest molecular mechanisms for auxin signaling in patterned cell differentiation.

Is the auxin influx carrierLAX3essential for plant growth and development in the model plantsMedicago truncatula, Lotus japonicusandArabidopsis thaliana?

“…These results are in agreement with the report of Mattsson et al [74], who established that the overexpression of MtLAX3 in A. thaliana leads to increased accumulation of auxin in the cells, which causes more cell divisions and bigger leaf surface.…”

Tobacco mosaic virus-directed reprogramming of auxin/indole acetic acid protein transcriptional responses enhances virus phloem loading

“…For TMV, our studies indicate that in mature tissue access to the vascular gateway is enhanced significantly by the disruption of select phloem-expressed Aux/IAA transcriptional regulators. Auxin, an essential plant hormone, is involved in many processes, including the development and regulation of the vascular network (45). Aux/IAA proteins are a key component in this regulatory system, playing a central role in converting auxin concentrations into gene expression (24,46).…”

Graft incompatibility in plants: Metabolic changes during formation and establishment of the rootstock/scion union with emphasis on Prunus species

“…In vascular regeneration experiments, when auxins were applied exogenously to stem segments, low concentrations (0.1%, w/w) of indole-3-acetic acid (IAA) stimulated phloem differentiation, whereas higher levels (1.0%, w/w) induced xylem differentiation (Aloni, 1995;2010). Likewise, in grafting experiments, an important group of substance involved in the development of compatible graft unions are the auxins released from the vascular strands of the stock and the scion, which induce the differentiation of vascular tissues, thus functioning as morphogenic substances (Aloni, 1987;Mattsson et al, 2003). Auxin translocation from the scion to the stock were found to accelerate the development of a successful graft union in Cactus (Shimomura and Fujihara, 1977).…”