Harnessing Genetic Variation in Leaf Angle to Increase Productivity of Sorghum bicolor

Abstract

The efficiency with which a plant intercepts solar radiation is determined primarily by its architecture. Understanding the genetic regulation of plant architecture and how changes in architecture affect performance can be used to improve plant productivity. Leaf inclination angle, the angle at which a leaf emerges with respect to the stem, is a feature of plant architecture that influences how a plant canopy intercepts solar radiation. Here we identify extensive genetic variation for leaf inclination angle in the crop plant Sorghum bicolor, a C4 grass species used for the production of grain, forage, and bioenergy. Multiple genetic loci that regulate leaf inclination angle were identified in recombinant inbred line populations of grain and bioenergy sorghum. Alleles of sorghum dwarf-3, a gene encoding a P-glycoprotein involved in polar auxin transport, are shown to change leaf inclination angle by up to 34°(0.59 rad). The impact of heritable variation in leaf inclination angle on light interception in sorghum canopies was assessed using functionalstructural plant models and field experiments. Smaller leaf inclination angles caused solar radiation to penetrate deeper into the canopy, and the resulting redistribution of light is predicted to increase the biomass yield potential of bioenergy sorghum by at least 3%. These results show that sorghum leaf angle is a heritable trait regulated by multiple loci and that genetic variation in leaf angle can be used to modify plant architecture to improve sorghum crop performance.KEYWORDS leaf angle; crop modeling; sorghum canopy; bioenergy sorghum; dwarf-3; P-glycoprotein; auxin transport S USTAINABLY increasing the productivity of crops on land currently used for agriculture without depleting natural resources is a global priority (Foley et al. 2011;Drewry et al. 2014). Improving the efficiency with which plants intercept solar radiation is one means to sustainably improve crop productivity. Leaf angle, or leaf erectness, is a plant canopy parameter that has drawn considerable attention because of the predicted improvement in photosynthetic efficiency and reduction in plant stress afforded by the redistribution of solar radiation from upper to lower levels of canopies (Tollenaar and Wu 1999;Duvick 2005;Murchie et al. 2009;Zhu et al. 2010;Murchie and Reynolds 2012;Drewry et al. 2014;Mansfield and Mumm 2014). Performance improvements predicted by theoretical models are corroborated by positive correlations between small leaf angles and cereal crop yields; post-green revolution rice cultivars have smaller leaf inclination angles and higher yields relative to their pre-green revolution predecessors (Yoshida 1972;Sinclair and Sheehy 1999;Sakamoto et al. 2006), and modern maize is also characterized by small inclination angles as a consequence of selection for increased grain yield in breeding programs (Duvick 2005;Lee and Tollenaar 2007;Hammer et al. 2009;Tian et al. 2011;Mansfield and Mumm 2014).Despite the association of leaf angle with increased productivity, its g...

3D sorghum reconstructions from depth images identify QTL regulating shoot architecture

“…The parents of the imaged RIL population, BTx623 and IS3620C, are fixed for nonfunctional and functional forms, respectively, of the Dw3 gene, which encodes an auxin efflux protein that has pleiotropic effects on stem elongation and additional architecture traits like leaf angle (Multani et al, 2003;Truong et al, 2015). A significant association between Dw3 and shoot cylinder height is not observed until the second time point (34 DAP), while different alleles of Dw3 introduce significant variability in leaf angle by the earliest time point (27 DAP).…”

“…A significant association between Dw3 and shoot cylinder height is not observed until the second time point (34 DAP), while different alleles of Dw3 introduce significant variability in leaf angle by the earliest time point (27 DAP). This is likely because Dw3 impacts height by impacting stem elongation and the stem has not yet begun to elongate substantially by the earliest time point; as such, the nonfunctional dw3 allele caused smaller leaf angles prior to any significant effect on stem elongation (Multani et al, 2003;Truong et al, 2015). Similar to Dw3, the effects of Dw2, a sorghum dwarfing gene on chromosome 6 near 42 Mb (but not yet cloned), are significantly associated with shoot cylinder height after the first time point (34, 39, and 44 DAP); unlike Dw3, Dw2 is not significantly associated with any other pleiotropic effects on leaf morphology.…”

“…Sorghum (Sorghum bicolor) is the fifth most produced cereal crop in the world and is a promising bioenergy feedstock . Recent work has demonstrated that optimization of plant canopy architecture has the potential to improve sorghum productivity (Ort et al, 2015;Truong et al, 2015). As such, we sought to develop an image-based platform to examine the genetic bases of shoot architecture traits in sorghum.…”

Transcriptome Profiling of Tiller Buds Provides New Insights into PhyB Regulation of Tillering and Indeterminate Growth in Sorghum

“…Energy sorghum hybrids tiller to a greater extent than grain sorghum genotypes, often producing canopies with excess leaf area index (greater than 7; Olson et al, 2012). A more optimal distribution of light interception could be achieved by growing energy sorghum with reduced propensity for tillering at lower plant density with leaves having reduced leaf angles (Truong et al, 2015). The reduced leaf area of low tillering varieties would conserve soil moisture for the grain-filling stage in drought-prone regions (Islam and Sedgley, 1981;Kebrom and Richards, 2013).…”

Morphological Plant Modeling: Unleashing Geometric and Topological Potential within the Plant Sciences

“…At the cellular level, root cortex cell number (Ron et al, 2013), the cellular basis of carpel size (Frary et al, 2000), and epidermal cell area and number (Tisné et al, 2008) have been analyzed. The genetic basis of cellular morphology ultimately affects organ morphology, and quantitative genetic bases for fruit shape (Paran and van der Knaap, 2007;Monforte et al, 2014), root morphology (Zhu et al, 2005;Clark et al, 2011;Topp et al, 2013;Zurek et al, 2015), shoot apical meristem shape (Leiboff et al, 2015;Thompson et al, 2015), leaf shape (Langlade et al, 2005;Ku et al, 2010;Tian et al, 2011;Chitwood et al, 2014a,b;Zhang et al, 2014;Truong et al, 2015), and tree branching (Kenis and Keulemans, 2007;Segura et al, 2009) have been described. Natural variation in cell, tissue, or organ morphology ultimately impacts plant physiology, and vice versa.…”