Fine mapping of a palea defective 1 (pd1), a locus associated with palea and stamen development in rice.

KEY MESSAGE : pd1, a genetic factor in a 69 kb region between RM11239 and RM11245 on rice chromosome 1, controls stamen number and palea development. Spikelets are important organs that store photosynthetic products in rice. Spikelet development directly affects grain yield and rice quality. Here, we report a palea defective (pd1) mutant identified from selfing progenies of indica cv. 93-11 after (60)Co γ ray treatment. pd1 mutant flowers only had four stamens (wild-type has six), but pollen fertility was not affected. Compared with 93-11 palea, pd1 mutant palea showed smaller and flatter leaf, which caused the lemma to bend excessively inward. pd1 mutants had only 46% seed setting rate and 21.6 g 1000-grain weight, which led to two-thirds loss of grain yield. Scanning electron microscope analysis revealed that pd1 mutants had reduced epidermal cell size and reduced numbers of fibrous sclerenchyma cells in both palea and lemma. To analyze the genetic factors involved, we crossed pd1 mutants with three japonica cultivars and generated F1 and F2 populations. The F1 phenotype and F2 segregation ratio indicated that a recessive gene controlled the mutant traits. Using the F2 population, we found that pd1 mapped between the simple sequence repeat markers RM11236 and RM11280 on rice chromosome 1. From a segregating population of 2836 plants, 77 recombinants were screened by RM11236 and RM11280. High-resolution linkage analysis narrowed the pd1 locus to a 69 kb region between RM11239 and RM11245 that contained 10 open reading frames (ORFs). Sequence alignment and quantitative real-time PCR expression analysis of these ORFs between 93-11 and pd1 mutant plants found no unequivocal evidence to identify the pd1 gene.