Genetics of canopy architecture traits in sorghum and maize

Abstract

Canopy architecture is a key determinant for the photosynthesis of a plant community. It influences the ability and efficiency of the plant community in intercepting the incident radiation and the conversion of the photosynthates into biomass, especially harvestable yield. The overall canopy architecture of a plant is determined by the combination of several complex traits, including stature (plant height) and the vertical pattern of the leaf inclination (leaf angle). The final height of an organism is controlled by multiple interacting genetic and environmental factors that occur during development. However, most genetic studies on sorghum plant height were based only on end-of-season measurement, overlooking a more complex and dynamic process. Here, we used time-series plant height data extracted from unmanned aerial vehicle (UAV) based imagery and functional mapping to investigate the dynamics of plant height genetics across development in two sorghum populations. Our finding revealed the contribution of persistent and transient quantitative trait loci (QTLs) in controlling the growth trajectories of the sorghum populations. Persistent QTLs control the variation in the overall growth trajectories of the two populations, whereas transient QTLs have small and temporary effects on the growth trajectories. These results demonstrate that we can leverage UAV-based high-throughput phenotyping and genomic technologies to decipher the genetic basis underlying the temporal dynamics observed in plant height across development and potentially mine useful transient QTLs. The vertical pattern of leaf angle across the canopy influences the penetration of solar radiation within the canopy and, ultimately, yield. Even though the maize ideotype was proposed to have a dynamic leaf angle pattern with upright leaves in the upper canopy and a gradual change to flat leaves in the lower canopy, the genetic basis underlying differential control of leaf angle across canopy levels has yet to be uncovered. Here, we used two doubled haploid (DH) populations with varying leaf angle patterns across the canopy. Some DH lines had a consistent leaf angle pattern, while others had a dynamic leaf angle pattern across the canopy. Combining univariate and multivariate QTL mapping analyses, we identified 20 QTLs controlling the variation observed in leaf angle across canopy levels. Some QTLs were canopy level specific, while others had either stable or dynamic effects across the canopy. Lastly, our findings showed that the correlation between leaf angle and grain yield varied based on the initial value of leaf angle at the four canopy levels covered in this study. The correlation was positive when the angle changed from flat to oblique or upright, and the correlation was negative when the leaf angle changed from oblique to fully upright, indicating that when the leaf becomes too vertical, it is not beneficial. Overall, these two projects involved the application of high-throughput phenotyping technology, growth curve modeling, linkage analysis, and genome-wide association study (GWAS) for identifying genetic loci controlling two canopy architecture traits in sorghum and maize. The two projects demonstrated the potential of employing an integrative approach to dissect the genetic basis of complex traits and gain new biological insights into two developmental features such as ontogeny and allometry in plants.