Snapshot Issue 8 March 2005

Semidwarf-1 protein

Little did the Augustinian monk Gregor Mendel (1822-1884) know that one of the traits he used to sort his green peas – and which he would use to found the laws of heredity – is one of the prime actors of what became known as the Green Revolution in the 1960s.

The green what? The Green Revolution or in other words ‘more rice for more mouths’. And what was at the heart of such a revolution? A dwarf-like variety of rice plant stemmed from cross-breeding. It soon became apparent that this under tall rice plant not only yielded more grain but it was less prone to being flattened by unfavorable weather conditions, which is always a hassle when it is harvesting time, and it also responded better to nitrogen fertilizers. As a result, within only a few decades, rice grain yield had doubled.

In 2002, researchers discovered the protein involved in this type of dwarfism: the semidwarf-1 protein also known as gibberellin 20 oxidase 2. Rice – like any living entity – needs growth hormones to grow. Only when the growth hormone pathway is tampered with, development is impaired. It so happens that wildtype gibberellin 20 oxidase 2 is a key enzyme in gibberellin biosynthesis, a plant growth hormone, and when this enzyme is deficient, the production of gibberellin is weakened and the rice plant does not grow so tall.

Interestingly, the semidwarf-1 protein is not the only mutant which meddles with gibberellin biosynthesis but it does happen to be the only one – so far – which lets the plant’s flowers develop and be fertilized normally because it does not interfere with the works of a second protein also involved in gibberellin biosynthesis and expressed in the plant’s reproductive tissues. Which, naturally, is an asset if you want the plant to have descendants.

The next step is to find ways of manipulating the synthesis of gibberellin in other crop plants so that their growth can be checked and with any luck their yield also increased. A far cry from Mendel’s approach but since then the world’s population has more than doubled…

Gibberellin 20 oxidase 1, Oryza sativa (Rice): P93771
Gibberellin 20 oxidase 2, Oryza sativa (Rice): Q8RVF5

L'édition française de cette chronique est disponible dans l'Instantanés du mois de Prolune.

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