Genetic Analysis And Gene Mapping Of A Marginal Albino Leaf Mutant Mal In Rice

Ninety-five percent of the rice yield comes from the photosynthesis, and leaf blade is the main organ of rice photosynthesis. The mutation of genes related to leaf color may change the structure and function of rice chloroplast, thus has important influence on photosynthesis. Consequently, the study of rice leaf color mutant is beneficial to reveal the photosynthesis molecular mechanism, and further to lay the foundation for increasing rice yield and quality.In this study, a rice marginal albino leaf mutant mal was obtainted from the progeny of rice(Oryza sativa L.) restorer line Jinhui10which was induced by ethyl methane sulfonate (EMS). Now, systematic studies for the mal will be done, including morphological characters, content of photosynthetic pigments, subcellular structure analysis, genetic analysis and gene mapping of the MAL gene. The main results were as follows:1. Morphological analysis of malThe mal leaf displayed albino margin since seedling stage and remained until the whole life. After the heading stage, the albino area of its three functional leaves increased from the up to down, namely, the flag leaf had the least albino area. Compared with the wild type, Plant height and each internode length of the mal is shortened significantly. What’s more, mal displayed narrow blade and the length of second leaf, third leaf deceased significantly. Also, most of important agronomic traits, such as number of effective panicle, grain number per panicle, filled grain number per panicle,1000-grain weight decreased significantly. However, number of panicle length and seed setting rate had no significant differences compared with those of the wild type.2. Analysis of photosynthetic pigment contentsPhotosynthetic pigment contents results showed that the photosynthetic pigment contents of mal mutant at seedling stage were significantly lower than that of the wild type. The content of photosynthetic pigment contents of the third leaf at the heading state was significantly reduced while the contents of flag leaf and second leaf have no apparent changes. Also, the contents of photosynthetic pigment decreased to the level of extremely significant differences for the second and third leaf margin parts than those of wild type at heading stage. However, the contents of the middle of second leaf and the middle of the third leaf had no apparent changes.3. Photosynthetic characteristics and chlorophyll fluorescence kinetic parametersIn mal mutant, the Fo and ETR had no apparent changes, while the Fv’/Fm’and qN were significantly higher than that of wild type. These results showed that light energy conversion efficiency and the original light energy capture efficiency of PS II reaction center in the mal mutant is higher, however, most of the light energy absorbed by its antenna pigment is lost in the form of heat, which leaded to the lower light energy utilization.Photosynthetic analysis showed that the Pn, Gs in mal is significantly lower, the Ci in mal is significantly higher, and the Tr almost had no differences compared with that of the wild type. Photosynthetic pigment is the necessary condition of plant photosynthetic. Reduction of Photosynthetic pigment of the mal may result in the decrease of net photosynthetic rate and cause accumulation of photosynthesis raw material CO2and H2O, Thus eventually led to the increase of intercellular CO2concentration.4. Cell structure analysisLeaves of the mal and JinhuilO at tillering stage were observed by transmission electron microscopy. The cells and chloroplasts in the green part of mal leaf developed normally as JinhuilO, Organelles were distributed evenly, chloroplast was packaged completely and distributed regularly stick to cell wall, and matrix was thick and matrix slices were well-ordered arranged. While in the albino part, the mesophyll cells were nearly hollow without obvious intact organelles and the chloroplast were fully degraded.5. Genetic analysisXinong1A was crossed with the mal for genetic analysis. The leaf color of F1progenies displayed normal green. In the F2progenies, the segregation ratio of normal leaf blades (4102) to mutant blades (1325) fitted the expected ratio of3:1(X2=0.69<x20.05=3.84), which suggested that the trait of mal was controlled by a recessive nuclear gene.6. Fine mapping of gene MALThe polymorphisms analysis between Xinong1A and the mal were first done with400pairs of SSR primers. Then, the MAL gene was mapped between RM310and RM6429on chromosome8. Within the region between RM310and RM6429,34new SSR markers and InDel markers were developed. Finally, the MAL gene was mapped between SSR marker M22and InDel marker ID27with genetic distance of0.22cM and0.73cM respectively, and approximately171kb for physical distance on chromosome8. According to gene functional annotation at the gramene website (http://www.gramene.org/Oryza_sativa/Location), there were33candidate gene in this region.