Lopez-Valdivia, I. | bioRxiv Science

bioRxiv2023

Cortical parenchyma wall width (CPW) regulates root metabolic cost and maize performance under suboptimal water availability

We describe how increased root cortical parenchyma wall width (CPW) can improve tolerance to drought stress in maize by reducing the metabolic costs of soil exploration. Significant variation (1.0 to 5.0 {micro}m) for CPW was observed within maize germplasm. The functional-structural model RootSlice predicts that increasing CPW from 2 to 4 {micro}m is associated with ca. 15% reduction in root cortical cytoplasmic volume, respiration rate, and nitrogen content. Analysis of genotypes with contrasting CPW grown with and without water stress in the field confirms that increased CPW is correlated with ca. 32 to 42% decrease in root respiration. Under water stress in the field, increased CPW is correlated with 125% increased stomatal conductance, 325% increased leaf CO2 assimilation rate, 73 to 78% increased shoot biomass, and 92 to 108% increased grain yield. CPW was correlated with leaf mesophyll midrib parenchyma wall width, indicating pleiotropy. GWAS analysis identified candidate genes underlying CPW. OpenSimRoot modeling predicts that a reduction in root respiration due to increased CPW would also benefit maize growth under suboptimal nitrogen, which requires empirical testing. We propose CPW as a new phene that has utility under edaphic stress meriting further investigation. Significance StatementSuboptimal water availability is a primary constraint for global crop production that is intensifying due to climate change. The metabolic cost of soil exploration is a critical factor in plant performance under suboptimal water availability. This study highlights how increased root cortical parenchyma wall width (CPW) reduces root metabolic cost and improves crop adaptation to water deficit. Modeling results also indicate that increased CPW would be beneficial under suboptimal nitrogen availability. Therefore, CPW is a promising target for breeding crops with improved water and nitrogen use efficiency.

plant biology↗

bioRxiv2022

Domestication and lowland adaptation of coastal preceramic maize from Paredones, Peru

Archaeological cobs from Paredones and Huaca Prieta (Peru) are phenotypically indistinguishable from modern maize. This contrasts with the earliest Mexican macro-specimens from Guila Naquitz and San Marcos, which are phenotypically intermediate even though they date more recently in time. These observations suggest at least two alternative scenarios, one in which maize was domesticated earlier than previously thought in the lowland Mesoamerica, followed by rapid lowland dispersal to Peru, and another in which maize was independently domesticated in South America and subsequently lost, as current evidence supports a single origin for all modern maize. To gain insights into the origins of ancient Peruvian maize, we sequenced DNA from three Paredones specimens dating 6775 to 5000 calibrated years before present (BP) and conducted comparative analyses with two teosinte subspecies (Zea mays ssp. mexicana and parviglumis) and extant maize, including highland and lowland landraces from Mesoamerica and South America. We show that Paredones maize originated from the same domestication event as Mexican maize and was domesticated by 6775 BP, implying rapid dispersal followed by improvement. Paredones maize show minimal levels of gene flow from mexicana, smaller than those observed in teosinte parviglumis. It also harbors significantly fewer alleles previously found to be adaptive to highlands, but not of alleles adaptive to lowlands, supporting a lowland migration route. Our overall results imply that Paredones maize originated in Mesoamerica, arrived in Peru without mexicana introgression through a rapid lowland migration route, and underwent improvements in both Mesoamerica and South America. Significance StatementThe coastal Peruvian preceramic sites of Paredones and Huaca Prieta provide the earliest known maize macro-remains. Found more than 3,800 km away from the maize center of origin and presenting a phenotypically modern cob constitution relative to their antiquity, these specimens represent a paradox for understanding maize evolution and dispersal. We show that Paredones maize originated in Mesoamerica, like all known maize, and arrived in South America without introgression from the teosinte mexicana. Since modern maize has substantial contributions from mexicana, it raises the question of when mexicana introgression spread to South America. Paredones maize preferentially shares adaptive allelic diversity with lowland Mesoamerican samples, suggesting a migration route probably associated with a coastal corridor previously identified with archeological findings.

plant biology↗