MOLECULAR BIOLOGY OF RICE
KO SHIMAMOTO
Rice (Oryza sativa L.) is a main food in many Asian countries where a large increase of the population is expected to occur in the coming 21st century. To meet the increasing demand for food supply in these regions, many efforts to improve rice varieties have been made in the past. More recently, rice is becoming a model crop for molecular biological studies because of the two reasons: 1) analysis of the rice genome is most advanced among cereals, and 2) transgenic plants are easily generated. With these two advantages, rice molecular biology has recently taken off and many exciting findings are being reported. Importantly, many fundamental findings obtained with rice could be used to improve cereals in the near future.
In this talk, I will first review current research activities in rice genomics. The advance in rice genomics gives a fundamental tool to analyze physiology and development of rice. Transposons can be used as tools for the elucidation of gene functions in rice. Examples of functional genomics using a transposon system will be presented.
Protection from diseases is one of the most important goals of the current plant biotechnology. For this end we recently identified rice genes which function as a molecular switch for disease resistance. The switch is a class of proteins called small GTP-binding protein, which are involved in signal transduction in many systems. Transgenic rice plants expressing a modified gene for the small G protein became resistant to infection by the rice blast fungus, one of the most important pathogen of rice. Currently we are trying to understand the signaling pathway for the disease resistance activated by this protein.
Another topic we have been working on is the photoperiodic control of flowering in rice. Rice is a typical short-day plant and flowering time is also a very important agricultural character of rice. Based on the analysis of mutations causing early flowering we identified the photoreceptor of plants, phytochromes, as the major photosensors determining flowering time. Because circadian clocks are known to be involved in regulation of flowering time, we also analyzed regulation of circadian clocks in rice. Results will be discussed.