Public Release: 

Plant response to light and stress

Cold Spring Harbor Laboratory

In ever-changing environmental conditions, the regulation of plant growth and development relies on precisely orchestrated cues provided by plant hormones. Two papers in the August 1 issue of Genes & Development highlight the importance of phytohormones, and lend valuable insight into the molecular mechanisms underlying plants' responses to light and stress.

BIG link between light signaling and auxin transport

Researchers from the Salk Institute have discovered an enormous link between light and auxin signal transduction pathways - 560 kiloDaltons, to be exact.

It was first noticed in the late1920s that changes in levels of the plant hormone, auxin, occur during light-regulated growth responses (ie., the phototrophic response, or the tendency of plants to grow towards the source of light). Until recently, though, genetic evidence linking plants' response pathways to light and auxin has been lacking.

Dr. Joanne Chory and colleagues discovered that two previously identified Arabidopsis muatnts - doc1, which displays abnormal expression of light-regulated genes, and tir3, known for its resistance to inhibitors of auxin transport - are actually two alleles of the same gene. This gene encodes a 560kD protein, which they aptly named "BIG." This work is of interest not only because BIG effectively bridges the gap between auxin- and light-mediated responses, but also due to the similarity that BIG displays to the Calossin gene family found in worm, flies and humans.

Putting out the fire: a role for IP3 in plant cell signaling

Researchers at the University of Arizona have made a significant advance in understanding how plants respond to stress.

The plant hormone abscisic acid (ABA) coordinates plant developmental programs with specific environmental stress responses by activating the expression of stress-adaption genes. Dr. Jian-Kang Zhu and colleagues have discovered that the molecule IP3 (inositol 1, 4, 5-triphosphate)acts as an intracellular messenger in the ABA- or stress-induced developmental pathways.

By engineering transgenic Arabidopsis plants to emit bioluminescense in response to ABA treatment or environmental stress, Dr. Zhu and colleagues identified the fiery mutation that renders plants hypersensitive to ABA, cold, drought or salt stress. After cloning the gene, they determined that fiery encoded a protein that degrades IP3.

Dr. Zhu's transgenic fiery mutants accumulate abnormally high levels of IP3 in response to ABA or stress, and thus display an enhanced expression of stress-adaption genes (along with a really bright luminescent signal - see attached figure). This work represents the first direct genetic evidence that IP3 acts as a second messenger in plants, mediating gene regulation by specific types of environmental stress.

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