Longer, deepwater rice crops are planted in South Asia and West Africa to survive floods. Shorter paddy rice varieties are widely cultivated worldwide because they are easier to harvest.

A key driver of plant growth is a hormone called gibberellic acid. It activates cell division in the stem tissue, causing the stem to lengthen. Breeders know they can control plant height by stimulating or inhibiting gibberellic acid activity. However, exactly how this works has been unclear.

Bioscientist Motoyuki Ashikari has been studying the growth and evolution of rice for years. He and a team of researchers conducted genetic studies and identified two genes that are involved in regulating rice plant growth.

"We showed that gibberellic acid is necessary, but not enough, for stem elongation," says Ashikari.

Interestingly, the two genes, calledACCELERATOR OF INTERNODE ELONGATION 1 (ACE1)andDECELERATOR OF INTERNODE ELONGATION 1 (DEC1), counteract each other as part of the regulation process.

In the presence of gibberellic acid, ACE1 stimulates cell division and elongation of the stem's 'internode' sections in deepwater rice. The shorter paddy rice variety did not have a functional ACE1 gene, but it did have a homologous ACE1-like gene that was switched on to activate stem elongation at a different point of plant development.

DEC1 was found in both the deepwater and paddy rice varieties. Its expression was reduced when deepwater rice plants were placed in deep water or treated with gibberellic acid. However, DEC1 continued to be expressed in paddy rice, even under the same conditions, suggesting this gene helps to suppress stem growth.

"We also found that ACE1 and DEC1 are conserved and functional in other plant species, like barley and other grasses, so our investigations improve understanding of the regulation of stem elongation in members of the Gramineae family that may have similar stem elongation mechanisms," says Ashikari.

The team next aims to understand stem elongation at the molecular level by identifying factors that are associated with ACE1 and DEC1 expression.