The Nitrogen Adaptation Strategy of the Wild Teosinte Ancestor of Modern Maize, Zea mays subsp parviglumis

Examination of wild ancestors can identify which traits have been altered by selection as possible targets for genetic improvement. We investigated the whole plant response to low nitrogen (LN), especially below ground, by the wild ancestor of modern maize (Zea mays L.), Balsas teosinte (Zea mays subsp. parviglumis H. H. Iltis & Doebley). Teosinte responded to LN by reducing the shoot N concentration and increasing the root: shoot biomass ratio. The lengths of individual crown roots and the total lateral root length increased, compensated by reduced crown root number. Low N caused a decrease in total root hair (RH) length and increased expression of high affinity nitrate transporters. To facilitate future mapping studies, these results were compared to a modern inbred ('W22') used as the parent in a modern maize x teosinte population and extensively employed in maize domestication studies. The adaptations to LN in teosinte and W22 were surprisingly conserved, but the strategies employed were often different. To reduce total RH length, teosinte reduced RH density whereas W22 reduced average RH length. To achieve reduced shoot biomass in response to LN, teosinte reduced tiller number and hence leaf number whereas W22 reduced average leaf size. Since tiller crown roots initiate from stem tissue, teosinte used tiller plasticity to reduce crown root number whereas modern maize reduced crown root number independently of tillering. We discuss the implications of these results for maize domestication.