Abstract
Premature senescence in annual crops reduces yield, while delayed senescence, termed stay-green, imposes positive and negative impacts on yield and nutrition quality. Despite its importance, scant information is available on the genetic architecture of senescence in maize (Zea mays) and other cereals. We combined a systematic characterization of natural diversity for senescence in maize and coexpression networks derived from transcriptome analysis of normally senescing and stay-green lines. Sixty-four candidate genes were identified by genome-wide association study (GWAS), and 14 of these genes are supported by additional evidence for involvement in senescence-related processes including proteolysis, sugar transport and signaling, and sink activity. Eight of the GWAS candidates, independently supported by a coexpression network underlying stay-green, include a trehalose-6-phosphate synthase, a NAC transcription factor, and two xylan biosynthetic enzymes. Source-sink communication and the activity of cell walls as a secondary sink emerge as key determinants of stay-green. Mutant analysis supports the role of a candidate encoding Cys protease in stay-green in Arabidopsis (Arabidopsis thaliana), and analysis of natural alleles suggests a similar role in maize. This study provides a foundation for enhanced understanding and manipulation of senescence for increasing carbon yield, nutritional quality, and stress tolerance of maize and other cereals.
Highlights
Agricultural productivity is essentially the amount of carbohydrates generated by photosynthetic assimilation of CO2 by plant leaves and stored into heterotrophic organs harvested for human/ industrial use
Maize diversity characterized in this study was captured in a panel that (1) includes maize lines from two major heterotic groups (Stiff Stalk Synthetic and Non-Stiff Stalk Synthetic), (2) includes only those inbred lines that flowered within a reasonable window in the midwestern United States, and (3) was genotyped by RNA sequencing (RNA-seq) of whole seedling mRNA (Hirsch et al, 2014)
Through systematic genomic and transcriptomic analyses, implementation of systems genetics (SysGen) framework, and experimental validations, we provide a broad model of senescence control and progression in a global staple crop
Summary
Agricultural productivity is essentially the amount of carbohydrates generated by photosynthetic assimilation of CO2 by plant leaves and stored into heterotrophic organs harvested for human/ industrial use. Improving the photosynthetic assimilation of crop plants is a viable approach to increase agricultural productivity. Most of the dry matter accumulating in grains of modern maize hybrids is fixed during the grain fill, with very little attributed to remobilization from organs developed during the pre-flowering period (Below et al, 1981; Cliquet et al, 1990; Ciampitti and Vyn, 2013). Selection for stay-green trait accounts for up to 63% of the total increase in dry matter accumulation in newer era hybrids released after the 2000s compared with older hybrids released in the 1930s (Lee and Tollenaar, 2007). The stay-green trait can have serious negative consequences such as delayed dry down resulting in higher moisture in the stover (leaves, stalks, and husk), which interferes with timely mechanical harvesting with combine harvesters (Yang et al, 2010)
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