Identification and gene mapping of a panicle apical abortion mutant (<italic>paa1331</italic>) in rice

Abstract

Rice panicle is an important agronomic organ which influences yield, and its development directly determines the yield potential. Over the past decades, a large number of genes related to grain size and grain number have been cloned, but there are few reports on cloning and function characterization of genes related to panicle development. We aim to explore the genes that regulate the degeneration of rice spike, improve the regulation network of panicle development, and provide theoretical basis for molecular breeding. In this study, a stably inherited mutant showing perturbed development of panicle ( panicle apical abortion 1331 ) was isolated from an ethyl methyl sulfate(EMS)mutagenized population of Yixiang 1B. Compared with the wild type, the mutant mainly showed a severe degeneration at the panicle tip (the affected florets account for as high as 53%), in addition to this, the plant height, tiller number and grain number were also affected. Observation on the development of panicle showed that the top spikelets of mutant paa1331 began to degrade during meiosis of the pollen mother cell, and the number of degenerated spikelets increased with the elongation of the young spike, distributing at the top of the first branch of the stem, while the number of degenerated spikelets showed a tendency to decrease gradually from top to bottom. Anatomical observations showed that the stamens of the mutant degenerated spikelets degenerated into linear, and the pulp was withered. The tissue section of mutant paa1331 and pollen staining assay showed that there were no pollen grains in the mutant anther, indicating that degeneration hindered the development of pollen; the vascular bundle of the mutant degenerated stem showed developmental defects, which may cause the transport of the material to be obstructed Trypan blue staining assay showed severe coloration of degraded spikelets on top of mutants, indicted that the panicle apical abortion was associated with programmed cell death. Hormone assay suggested that the IAA content of mutants was higher than that of wild type. Genetic analysis showed that mutant trait was controlled by a recessive gene. Combined the analysis of map-based cloning and De novo genome sequencing, we found one gene LOC_Os04g40720 , of which the fourth exon has an A-to-G single base substitution, which resulted in a change from Asn to Asp. At present, this gene has not been reported to confer function in panicle development, thus we treated it as candidate gene.