Rice lax panicle (lax) mutant had defect in early inflorescence differentiation and lateral branch formation and exhibitedfewer numbers of rachis branches and spikelets in the panicle. The mutant also had abnormality in floral organ formation. Whereas, the spotted leaf 6 (spl6) mutant produced lesions in absence of pathogen. Analysis with a lax spl6 double mutant indicated both genes are controlled by single recessive factor and linked on chromosome 1 with 7 centiMorgan map distance. The lax gene was fine mapped within the 261.3 kb region between RM7594 and RM5389 that predicted 10 open reading frames (ORF) as candidate for lax gene. Sequencing of the candidates in the lax mutant revealed a substitution of nucleotide T by G corresponding to an amino acid substitution from serine (S) to alanine (A) at the 117th position within the coding region of the candidate ORF bhlh123. The intronless 1080 bp cDNA of LAX gene contains an ORF of 215 amino acids and encoded a basic helix-loop-helix transcription factor. Analysis of a 5.1 kb genomic fragment of the lax gene from homozygous dominant progeny which corresponded to indica cultivar resulted in a long deletion of 24 nucleotides in the upstream of LAX cDNA. (This research was supported by the National Research foundation of Korea, Grant 0070065).

• Mohammad Nurul Matin(Department of Biotechnology, Yeungnam University)
• Sang Gu Kang(Department of Biotechnology, Yeungnam University) Corresponding author