Rice Genetics Newsletter, Vol. 18

Rgn18

4.	msp1 mutant aberrant for archesporial cell division in the anther and ovule of rice
	K. I. NONOMURA.¹, K. MIYOSHI¹, M. EIGUCHI¹, A. MIYAO², H. HIROCHIKA² and N. KURATA^1,3 1)National Institute of Genetics, Mishima, Shizuoka, 411-8540 Japan 2)National Institute of Agrobiological Science, Tsukuba, Ibaraki, 305-8602 Japan 3)School of Life Science, Graduate University for Advanced Studies, Mishima, Shizuoka, 411-8540 Japan

Our study aims to elucidate the gene network regulating the reproductive processes of higher monocot plants. A completely sterile mutant of rice (Oryza sativa L.) was induced by suspension culture and regeneration of embryonic calli. The sterile phenotype segregated according to Mendelian fashion of a recessive gene in F₂ generation (148:37). This recessive gene seems to affect the proliferation of germ cells in both male and female organs. We designated this gene as msp1 (multiple sporogenous cells 1).

Anther elongation was severely affected in msp1 mutant (Fig. 1). Paraffin embedded sections of mutant anthers at meiosis revealed the following characteristics: (1) increase in the number of pollen mother cells (PMCs) approximately 40% more than that of wild type (173 +or- 21 PMCs in msp1 and 126 +or- 14 in WT per anther locule), (2) lack of tapetal cell layer (Fig. 1B) and (3) unelongated epidermal cells (Fig. 2B). In addition, development of PMCs was arrested at early meiotic stage (data not shown). Megaspore mother cells (MMCs) are usually larger and less-stained than surrounding cells in an ovule (Fig. 2C), whereas multiple MMC-like cells were observed in a mutant ovule (Fig. 2D). However, msp1 mutant pollinated with normal pollens showed partial fertility (data not shown), indicating that this mutant can partially induce functional embryo sac.

The sporogenous cells and three wall layers, endothecium, middle layer and tapetum, are derived from three successive periclinal divisions of archesporial cells in anther primordium (Davis 1966). The increased PMCs/MMCs and lack of tapetum cell layer simultaneously found in msp1 mutant flowers suggest that Msp1 gene acts during archesporial cells being differentiated into sporogenous cells and wall layers in young anthers and limits the proliferation of germ cells in both reproductive organs.

Acknowledgments

This research was supported by Program for Promotion of Basic Research Activities for Innovative Biosciences.

References

Davis, G. L., 1966. Systematic Embryology of the Angiosperms. John Wiley & Sons, New York.