Genetic and brassinosteroid control underlying leaf angle variation across the canopy in sorghum

Leaf angle, the inclination between the midrib of a leaf blade and the stem, is one of the main determinants of crop productivity. Plants with an upright leaf angle on the top and more horizontal towards the bottom can maximize their light interception and photosynthetic capacity, increasing yield per plant and unit of land. Experiments to investigate the genetic control of leaf angle have been routinely designed on the use of one or two arbitrarily selected leaves, or merged the data from multiple leaves on an average value. This approach has limited our understanding of the control of leaf angle at different layers of the canopy. Therefore, we performed GWAS and QTL mapping to dissect the genomic control of this complex trait in sorghum, using classical and novel phenotyping strategies. Our findings demonstrate that there are regions controlling leaf angle across the canopy, and chromosomal intervals associated with the trait at specific sections of the canopy. The use of several populations allowed us to dissect the previously reported QTL on chromosome 7, demonstrating the presence of three intervals, one affecting angle over all layers and two only associated with the middle canopy. Additionally, our research focused on the biological effects of brassinosteroids (BRs) on leaf angle, demonstrating that the application of a BR inhibitor, propiconazole (pcz), induced changes in leaf angle, other plant architecture traits, and the pattern of expression of several BR genes. Our data revealed that the levels of BZR1/BES1 expression in collars are highly correlated with leaf angle, suggesting that this transcription factor is a good target for further investigation, to change the current distribution of leaf angle in sorghum. Finally, we provided evidence of a cross-talk between BRs and auxin based on the comparative analysis of BZR1/BES1 and Dw3 expression levels. Our discoveries have generated novel information that could be exploited for the improvement of leaf angle distribution in the sorghum canopy, to increase crop productivity and respond to future demands of food, feed, fiber and fuel