Genes that underlie natural variation in growth rate and flowering time in local accessions of Arabidopsis thaliana
Malik, Zafar Iqbal
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Growth rate and flowering time are agriculturally important traits that are linked to fitness, productivity and reproductive success of plants. To study the genetic basis for natural variation in growth rate and flowering time between local accessions of Arabidopsis thaliana, hybrids were produced between fast growing / late flowering and slow growing / early flowering parents. F3 and F5 hybrid families were grown under a range of conditions – under a constant controlled environment, outside over the winter and outside in spring and early summer. Growth rates were estimated from repeated images of rosettes. Flowering time, as number of leaves to flower, was also recorded both in control and natural conditions for F5 lines. Damage by slugs and stress-induced production of anthocyanin pigments were also recorded for plants grown outside. Broad-sense heritability estimates were higher for F5 families than F3, in which more loci will segregate, and ranged from 48% to 89%. No significant correlation between growth rates under different environments was observed in most cases for F3 populations, however significant correlations were detected for F5 families outside and under controlled conditions, suggesting that same genes can affect growth rate in more than one environment. The genotypes of F3 families were determined at thirty-nine SSLP (simple sequence length polymorphism) loci and used in regression with phenotype data to search for quantitative trait loci (QTL). Significant QTLs were detected in F3 families for growth rate, flowering time and anthocyanin production, but not for herbivore damage. To confirm QTL detected in the F3 and to detect additional loci, bulk segregant analysis was carried out in F5 families grown under different conditions. Potentially linked markers were tested further in individual F5 plants and QTL mapped on a finer scale in F5 families that remained heterozygous for candidate regions. VIP5 and LDL1 were selected as potential candidate genes for flowering time variation. These genes were sequenced for two parental alleles. A transposon insertion and 5’ UTR deletion were found in the LDL1 allele from the late flowering parent and SNPs (single nucleotide polymorphisms) were observed throughout the gene. However both alleles appeared to be expressed at similar levels. Transgenic lines have been produced carrying the LDL1 allele from the early flowering parent (4D1) in the background of the later flowering parent (11C1). This work is on-going and will hopefully reveal whether LDL1 underlies differences in flowering behaviour seen between 11C1 and 4D1.