Genetic Control of Switchgrass Flowering Time and Relationship to Growth and Quality

Megan Sue Taylor, Purdue University


Switchgrass is a native prairie grass that has been identified as a key biofuel crop world-wide. The utilization of switchgrass for bioenergy depends on the suitability of the plant material and the amount of biomass that can be produced. Flowering and development are key factors that affect biomass accumulation and plant material suitability for biofuel production. The goals of this thesis were to 1) determine genetic control of switchgrass flowering time within four sibling populations, 2) determine differenitally expressed genes for flowering time between parents and offspring, 3) determine genetic control of growth traits within a F2 switchgrass population, and 4) understand relationships between growth, development, and quality traits. A total of 37,901 single nucleotide polymorphisms were obtained from 586 individuals from the populations by exome capture sequencing. A genome wide association study identified five significant signals at multiple loci including three for heading and two for anthesis. Among them, a homolog of FLOWERING LOCUS T on chromosome 5b associated with heading date was identified at the Lafayette location across two years. A homolog of ARABIDOPSIS PSEUDO RESPONSE REGULATOR 5, a light modulator in the circadian clock associated with heading date was detected on chromosome 8a across locations and years. Using transcriptome profiling of parents and progeny key members of the circadian rhythm pathway were identified and differentially expressed between early and late genotypes, including PSUEDO RESPONSE REGULATOR 5 and 7 (PRR5 and PRR7) controlling late flowering and CONSTANS (CO), FLOWERING LOCUS T (FT), and TIMING OF CAB 1 (TOC1) controlling early flowering. PRR5 and FKF1 were upregulated in both early flowering and late flowering genotypes. CYP76C2, a P450 cytochrome gene, was upregulated with high expression in only the late flowering parent. Key transcription factors of ELONGATED HYPOCOTYL 5 (HY5) and LATE ELONGATED HYPOCOTYL (LHY) were downregulated within early flowering and late flowering genotypes. PHYTOCHROME INTERACTING FACTOR 3 (PIF3) and the CO TF family were upregulated in early flowering genotypes and downregulated in late flowering genotypes. Four QTLs were detected for height (HT), canopy diameter (CD), and biomass yield (BY) in 2015 or 2016, with LOD scores ranging from 4.90 to 8.17 and percent variance explained (PVE) ranging from 7.1% to 12.9 %. A significant QTL for HT was identified on Chr 2b in both 2015 and 2016. A QTL for CD in 2015 and BY in 2016 was co-localized on Chr 2a. Within the confidence interval for the QTL on Chr 2a for CD in 2015 a BRASSINAZOLE-RESISTANT1 (BZR1) gene was identified. A significant QTL for CD was detected on Chr 5b and contained an AUXIN-RESPONSIVE GH3 family protein (DFL1) within the confidence interval. On average stem and leaf make up 78% and 21%, respectively, of the total plant biomass across 249 switchgrass samples. Significant correlations existed between development traits and quality traits. Anthesis was positively correlated with total sugar content, nitrogen, and in vitro dry matter digestibility but negatively correlated with acid detergent lignin and acid detergent fiber for whole plant samples across population. A strong positive relationship was observed between biomass and ertherified ferulates within whole plant samples.




Jiang, Purdue University.

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