Plant, Animal & Microbe Genomes X Conference

January 12-16, 2002
Town & Country Convention Center
San Diego, CA

Workshop: Arabidopsis
          

NATURAL VARIATION OF LIGHT RESPONSES AND FLOWERING IN ARABIDOPSIS

¹ Max Planck Institute for Developmental Biology, D-72076 Tuebingen, Germany, and Salk Institute, La Jolla, CA 92037, USA

² Salk Institute, La Jolla, CA 92037, USA

³ Howard Hughes Medical Institute and Salk Institute, La Jolla, CA 92037, USA

⁴ UC San Diego, La Jolla, CA 92093, USA

We are exploiting the natural variation found in Arabidopsis accessions to identify new loci or special alleles of known genes that are involved in light response and flowering. Wide genetic variation was seen when hypocotyl lengths were compared between 140 Arabidopsis accessions exposed to five light conditionsÐwhite, blue, red, far-red light, and darkÐ, and three hormone conditionsÐgibberellins (GAs), brassinazole (a brassinosteroid biosynthesis inhibitor), and ethylene. Cluster analysis was used to compare accessions with known photoreceptor mutants. One accession, Lm-2, clustered with the phyA photoreceptor mutant. Subsequent molecular and biochemical analysis showed that Lm-2 carries and unusual phyA allele.

Similar variation was seen when Arabidopsis accessions were surveyed for flowering time under long days (with and without vernalization) and short days. Previous work by Caroline Dean and colleagues (Johanson et al., Science 290, 344; 2000) has identified the FRI locus as an important determinant of flowering time and vernalization response in natural accessions. We genotyped all our accessions for the presence of Columbia and Ler-type deletions at FRI, and found at least one accession that flowers late and is strongly vernalization-responsive, but apparently lacks a functional FRI allele, indicating that this accession regained vernalization sensitivity through a secondary mutation.

We also used the Niederzenz/Columbia recombinant inbred lines (RILs) produced by Eric Holub and colleagues to map Quantitative Trait Loci (QTL) for flowering in short days. We generated an AFLP-based map to genotype RILs, and used it to map a major QTL controlling flowering. This QTL, FLOWERING1, appears to be due to a deletion of a MADS-box gene affecting flowering time.