Trends in Plant Science
ReviewFrom dwarves to giants? Plant height manipulation for biomass yield
Section snippets
A new paradigm in crop architecture
Biofuels have been proposed as an alternative to meet the increasing energy demand, to control high prices of fossil fuels and to reduce emission of greenhouse gases responsible for climate change (National Biofuels Action Plan, http://www1.eere.energy.gov/biomass/pdfs/nbap.pdf) 1, 2. In 2008, 9.2 billion gallons of ethanol were produced in the US (Renewable Fuels Association – 2009 Monthly US Fuel Ethanol Production/Demand, http://www.ethanolrfa.org/industry/statistics/#B), and even though the
Gibberellins
GAs represent a large group of cyclic diterpene compounds that promote stem elongation. Mutants in GA synthesis or signaling show dwarf phenotypes. In fact, mutations in GA-related genes are responsible for the semi-dwarf habit associated with the green revolution 7, 8. GA metabolism and signaling are both crucial for controlling PHT.
Brassinosteroids
BRs are another family of plant hormones that promote plant growth [25]. Consistent with a main function of BRs in promoting cell elongation, mutants defective in BR biosynthesis or signaling display dwarf phenotypes. By contrast, increased BR levels or activity can increase plant size, biomass and seed yield. BR biosynthesis and signaling pathways are well-established 26, 27, 28, 29, 30.
Quantitative genetics of PHT
PHT is polygenic in maize. More than 100 QTLs have been reported with a minimum of 40 different positions involving all ten chromosomes in the genome [42], and up to 30 QTLs have been detected in a single mapping experiment [43]. Large-scale, high-resolution mapping experiments, such as those using nested association mapping (NAM) [44], are currently underway, so the number of distinct QTLs affecting PHT is likely to increase in the near future.
QTLs identified from individual mapping studies
Pleiotropic effects of PHT on other traits
One of the most important considerations in manipulating PHT for biomass production is the pleiotropic interactions and, therefore, the potential risk of undesirable consequences that changes in PHT might have on other important traits.
Strategies for manipulation of PHT for biomass production
Increasing PHT is the most obvious and direct way to impact biomass yield, although not the only one. The modification of traits such as leaf angle or tissue density could also potentially increase biomass yield on a per plot basis. We have summarized some of the most important QTLs, enzymes and candidate genes with potential to impact PHT and, therefore, lignocellulosic feedstock production.
QTLs usually encompass many genes and are often complex or confounded by pleiotropy. Dwarf mutants
Acknowledgements
Research in the authors’ laboratories is supported by the Iowa State University Plant Science Institute, the National Science Foundation (grant IOS-0546503 to Y.Y.), the US Department of Agriculture National Research Initiative (grant 2006–01163 to P.W.B.) and the R.F. Baker Center for Plant Breeding at Iowa State University (to M.G.S.F. and T.L.).
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