Identification And Gene Mapping Of A Thermo-Sensitive Leaf-Color Mutant T8408in Rice

Chlorophyll is the important pigment involved in photosynthesis in plant chloroplasts. The biosynthesis of the chlorophyll is a very complicated process. The metabolism of chlorophyll is influenced when certain aberrance happens to some loci of the plant genome, which leads to the change of leaf color subsequently. The chlorophyll-deficit mutants of rice are not only the materials of the research on the photosynthesis of higher plants, the biosynthesis and genetic differentiation of chlorophyll, but also used in rice heterosis as a selection marker. Therefore, the exploitation, research and utilization of leaf color mutants in rice have been highlighted all the time.In addition to the leaf color phenotype, the color of panicles is also influenced in certain leaf color mutants besides the phenotype character of leaf color, which shows white panicles. However, there are few reports about white panicle so far.In this paper, a thermo-sensitive leaf-color mutant T8408has been identified from the T-DNA insertional mutant lines of Nipponbare. The morphological characters, physiological characteristics and chloroplast ultrastructure of this white panicle mutant were studied. Genetic action of the mutant was analyzed using the F1and F2progenies from T8408crossed with normal green wild type Nipponbare and another indica line variety IR36. Furthermore, this mutant gene, which was temporarily designated wp3, was fine mapped with microsatellite markers and self-developed Indel markers. Then gene prediction was carried out within the located region. The main results are as follows:1. The phenotype of the thermo-sensitive leaf-color mutant T8408is that the albino is presented in the basal leaves at the seedling stages. This character stays in basal leaves until the beginning of tillering stages. Then the leaves of whole plant turn albino gradually. Meanwhile, the panicles of the plant are white at the heading early stage, and the phenotype return normal during the later part of grain ripening.2. The measurement of the chlorophyll content of the wild type and T8408treated in different temperatures showed that the degree of albino enhanced obviously with the temperature increasing. In20℃and25℃, the white phenotype can only be observed on the sheaths and blades of the1st complete leaves. and In30℃, it can also be seen on few margin of the2nd leaves. However, while in35℃, the whole plants of the mutant perferms albino. It is suggested that the expression of this gene is regulated by temperature to certern extent.3. The observation results of the chloroplast ultrastucture by transmission electron microscope revealed that the inner structure of the chloroplast changed significantly, less numbers of grana and grana lemma could be seen in some cells, with some vesicle-like structures. However, only a large number of vesicle-like structures and osmiophilic bodies instead of grana could be observed. These all indicated that the thylakoid membrane system of different cells in the same leaf degradated in varying degree.4. Reciprocal cross was made between T8408and Nipponbare, the leaf color of F1was normal, and the proportion of normal to albino in F2was3:1, which revealed that the phenotype in this mutant is controlled by a single recessive nuclear locus. Besides, the mutant perferms albino on both panicles and leaves, suggested that wp3shows pleiotropic effect.5. The preliminary mapping of wp3using269recessive plants from F2progeny by crossed T8408with IR36showed that it was located to the long arm of chomosome8, about6.4cM from the centromere. The gene was further restricted between Inde15and Inde16at a interval of161kb physical distance using a larger population and some self-designed Indel markers.