July 29, 2004 In looking for clues to the identity of a mysterious new plant hormone, a research team lead by Ottoline Leyser of the University of York has come one step closer in finding a gene required for the hormone's synthesis. The biochemical activity of this synthesis protein potentially offers a significant clue to the nature of the hormone, which is thought to coordinate rates of growth between different plant tissues.
In plants, as in animals, communication between different parts of the body is vital if the left hand is to know what the right hand is doing. In animals, this is achieved by a combination of the nervous system and hormone signals. Plants don't have a nervous system, so hormonal signals have a greater role to play. Darwin was instrumental in discovering the first known plant hormone, auxin, and since then a handful of additional long-distance chemical messengers have been found in plants. This number is surely insufficient to accomplish the complex coordinated progression of a plant through its life cycle and the plant's diverse responses to changing environmental conditions. Many plant biologists therefore believe that there are more plant hormones out there waiting to be discovered.
Recent results from work on pea, petunia, and the small weed Arabidopsis have suggested the existence of one such novel plant hormone. The main role of this hormone is to regulate the degree of shoot branching. The hormone is apparently made throughout the plant, but hormone made in the roots is able to travel up the plant to influence branching in the shoot, suggesting that it may play a role in balancing root and shoot growth.
In this issue of Current Biology, Ottoline Leyser and co-workers describe the identification of a gene that is essential for the synthesis of this novel hormone. The gene encodes a protein that they show can cleave carotenoids, such as the chemicals responsible for the orange pigment in carrots. This suggests that the new hormone is a carotenoid derivative, and this will help in the hunt for its identity.
Jonathan Booker, Michele Auldridge, Sarah Wills, Donald McCarty, Harry Klee, and Ottoline Leyser: "MAX3/CCD7 Is a Carotenoid Cleavage Dioxygenase Required for the Synthesis of a Novel Plant Signaling Molecule"
Published in Current Biology, Volume 14, Number 14, 27 July 2004, pages 1232-1238.
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