Plant sciences: Breeding the top of the crops

Elite crops can be bred to maintain their current high yields with less fertilizer, are reported in a paper published online this week in Nature. The finding, which could aid efforts towards reaching sustainable global food security, sprouts from a deeper-rooted understanding of how plants metabolize nitrogen.

The so-called ‘green revolution’ of the 1960s increased agricultural yields and mitigated food shortages. Crops developed at this time provided higher-than-normal yields because their growth was intentionally stunted and the shorter heights reduced the risk that the plants would be flattened by wind or rain. Modern elite rice and wheat crops still retain this tendency towards semi-dwarfism.

At the same time, however, such crops are less efficient at using nitrogen - an apparent side effect of a growth-inhibiting protein called DELLA, the breakdown of which is inhibited in green revolution varieties. This necessitates the application of high doses of environmentally unfriendly, nitrogen-based fertilizers to compensate. However,the mechanisms underlying the nitrogen-use efficiency of cereals have remained uncertain.

Xiangdong Fu and colleagues surveyed differences in nitrogen uptake in green revolution varieties of rice. They find a relationship between uptake levels and the gene that encodes the growth-regulating transcription factor GRF4, which has the opposite effect of DELLA. GRF4 and DELLA exist in a balance that regulates plant growth and nitrogen metabolism. By tipping the scale in favour of GRF4, the authors demonstrate that green revolution variety rice and wheat can be produced that not only have improved nitrogen-use efficiencies, but also maintain their characteristic semi-dwarfism and high yields.