Abstract
The architecture of a plant affects its ability to compete for light and to respond to environmental stresses, thus affecting overall fitness and productivity. Two components of architecture, branching and height, were studied in 182 F7 recombinant inbred lines (RILs) at the vegetative, flowering and mature developmental stages in the panicoid C4 model grass system, Setaria. The RIL population was derived from a cross between domesticated S. italica (foxtail millet) and its wild relative S. viridis (green foxtail). In both field and greenhouse trials the wild parent was taller initially, started branching earlier, and flowered earlier, while the domesticated parent was shorter initially, but flowered later, producing a robust tall plant architecture with more nodes and leaves on the main culm and few or no branches. Biomass was highly correlated with height of the plant and number of nodes on the main culm, and generally showed a negative relationship with branch number. However, several of the RILs with the highest biomass in both trials were significantly more branched than the domesticated parent of the cross. Quantitative trait loci (QTL) analyses indicate that both height and branching are controlled by multiple genetic regions, often with QTL for both traits colocalizing in the same genomic regions. Genomic positions of several QTL colocalize with QTL in syntenic regions in other species and contain genes known to control branching and height in sorghum, maize, and switchgrass. Included in these is the ortholog of the rice SD-1 semi-dwarfing gene, which underlies one of the major Setaria height QTL. Understanding the relationships between height and branching patterns in Setaria, and their genetic control, is an important step to gaining a comprehensive knowledge of the development and genetic regulation of panicoid grass architecture.
Highlights
Almost all plants branch, in order to develop an architecture that will enable them to capture and compete for resources
The S. viridis parent was taller than the S. italica parent in both trials, and 33% of the recombinant inbred lines (RILs) in the greenhouse trial and 44% of the RILs in the field trial had heights that showed transgressive segregation by being either shorter than the S. italica parent or taller than the S. viridis parent (S1 and S4 Figs)
Tiller number at the vegetative stage was measured in both trials but only one plant had a tiller in the plants destined for the field trial, presumably because vegetative measurements for this trial were taken three days earlier than for the greenhouse trial
Summary
In order to develop an architecture that will enable them to capture and compete for resources. The ability of a plant to modify its architecture by differential branching and elongation is a characteristic that is determined both by developmental genetic. There are two main types of branching, tillers that emerge from buds in the axils of nodes that are crowded together at the base of the plant, and aerial branches that originate from nodes above elongated internodes [11,12,13,14,15,16,17]. Tillers are produced by all wild grasses, and generally these tillers directly recapitulate the development of the main culm by producing adventitious roots that can eventually allow them to become semi- or fully independent plants [18]. When aerial branches are present, they can initiate on the main culm and/or on tillers, and in some species, multiple orders of aerial branches may be produced
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