The rice photoperiod sensitivity gene Hd6 encodes protein kinase CK2
alpha
Yuji Takahashi1, Takuji Sasaki2 and Masahiro Yano2
1
Institute of the Society for Techno-innovation of Agriculture, Forestry and Fisheries,
Tsukuba, Ibaraki 305-0854, Japan 2Department of Molecular Genetics, National
Institute of Agrobiological Resources, Tsukuba, Ibaraki 305-8602, Japan
Several quantitative trait loci (QTLs) controlling heading date in rice have been
identified in a population derived from a cross between the japonica variety
Nipponbare and the indica variety Kasalath. In backcross progeny from the same cross,
Hd6 was detected on the long arm of chromosome 3, but it was not detected in the F2
population. At the Hd6locus, the Kasalath allele is semi-dominant and increases the
number of days-to-heading. A day-length-treatment test of a nearly isogenic line (NIL)
of Hd6 revealed that Hd6 is involved in photoperiod sensitivity. A genetic analysis
using NILs revealed an epistatic interaction between Hd6 and another QTL that
controls heading date, Hd2. We used a large segregating population for the
high-resolution and fine-scale mapping of Hd6. We also constructed genomic clone
contigs around the Hd6 region. As a result, we delimited Hd6 to a 26.4-kb genomic
region, and identified a gene encoding the alpha subunit of protein kinase CK2 (CK2
alpha) in this region. The Nipponbare allele of CK2 alpha contains a premature stop
codon; the resulting truncated product is undoubtedly non-functional. In genetic
complementation analysis, the Kasalath allele of CK2 alpha increased days-to-heading.
We conclude that Hd6encodes CK2 alpha. Previous studies in Arabidopsis have
revealed the involvement of CK2 in the transcriptional regulation of multiple genes,
including some light-regulated genes and genes controlling circadian rhythm. Our
results clearly indicate that CK2 alpha plays a role in controlling plant photoperiod
sensitivity.