Salazar-Vidal, M. N. | Search bioRxiv

bioRxiv2021

A B73 x Palomero Toluqueo mapping population reveals local adaptation in Mexican highland maize

Generations of farmer selection have produced a unique collection of traditional maize varieties adapted to the environmental challenges of the central Mexican highlands. In addition to agronomic and cultural value, Mexican highland maize represents a good system for the study of local adaptation and acquisition of adaptive phenotypes under cultivation. In this study, we characterized a recombinant inbred line population derived from the cross of the B73 reference line and the Mexican highland maize variety Palomero Toluqueno. Evaluation over multiple years in lowland and highland field sites in Mexico identified genomic regions linked to yield components and putatively adaptive morphological traits. A region on chromosome 7 associated with ear weight showed antagonistic allelic effects in lowland and highland fields, suggesting a trade-off consistent with local adaptation. We identified several alleles of highland origin associated with characteristic highland traits, including reduced tassel branching, increased stem pigmentation and the presence of stem macrohairs. The oligogenic architecture of characteristic morphological traits supports their role in adaptation, suggesting they have arisen from consistent directional selection acting at distinct points across the genome. We discuss these results in the context of the origin of phenotypic novelty during selection, commenting on the role of de novo mutation and the acquisition of adaptive variation by gene flow from endemic wild relatives.

plant biology↗

bioRxiv2020

Low nitrogen availability inhibits the phosphorus starvation response in maize (Zea mays ssp. mays L.)

BackgroundNitrogen (N) and phosphorus (P) are macronutrients essential for crop growth and productivity. In cultivated fields, N and P levels are rarely sufficient, contributing to the yield gap between realized and potential production. Fertilizer application increases nutrient availability, but not all farmers have access to fertilizers, nor are current rates of application sustainable or environmentally desirable. Transcriptomic studies of cereal crops have revealed dramatic responses to either low N or low P single stress treatments. In the field, however, levels of both N and P may be suboptimal. The interaction between N and P starvation responses remains to be fully characterized. ResultsWe characterized growth and root and leaf transcriptomes of young maize plants under nutrient replete, low N, low P or combined low NP conditions. We identified 1,555 genes to respond to our nutrient treatments, in one or both tissues. A large group of genes, including many classical P starvation response genes, were regulated antagonistically between low N and P conditions. An additional experiment over a range of N availability indicated that a mild reduction in N levels was sufficient to repress the low P induction of P starvation genes. Although expression of P transporter genes was repressed under low N or low NP, we confirmed earlier reports of P hyper accumulation under N limitation. ConclusionsTranscriptional responses to low N or P were distinct, with few genes responding in a similar way to the two single stress treatments. In combined NP stress, the low N response dominated, and the P starvation response was largely suppressed. A reduction in N availability was sufficient to repress the induction of P starvation associated genes. We conclude that activation of the transcriptional response to P starvation in maize is contingent on sufficient N availability.

plant biology↗