Physiological Analysis Of A Lesion Mimic Mutant And Map-based Cloning Of Gene LM In Rice(Oryza Sativa L.)

In this paper, a lesion mimic mutant in rice was isolated from the rice T-DNA insertion populationconstructed by our lab. The mutant was used to observe the physiological characters and map the mutantgene. Finally, using map-based cloning we cloned the LM gene encoding a P450monooxygenase whichis an essential enzyme involving in plant serotonin biosynthesis pathway. The loss-of-function of LMleads to the lesion mimic phenotype. Results from our paper are summarized as follows:1. From observation through a lesion mimic rice mutant, the formation of the lesion began in theperiod of three leaves. Then the leaves on the mutant performed the expansion of the lesion square andthe formation of new lesions. Formation of different temperature on lesion studies indicated that theformation of lesion had no relation with temperature. Lesion leaves DAB research indicated that PCDwas emerged on the mutant leaves due to the increase of active oxygen.2. The ROS metabolism studies have shown that SOD activity, POD activity and MDAaccumulation in mutant plants was significantly increased compared with wild type plants. It isestimated that the accumulation of ROS in the mutant plants is obvious, which induce the activity ofSOD and produce H2O2. The increase of H2O2stimulated the POD activity. The accumulations of activeoxygen compound in the cell undermine the balance of ROS in normal cell. Unsaturated fatty acids inthe membrane lipid bilayer are oxidized significantly and produce MDA. Then the bilayer in leave cellwas significantly injured.3. The photosynthetic characteristics research has shown that SPAD, F0, Fm, F0’, Fm’ and Fv’/Fm’rate of mutant leaves increased significantly compared with wild type. However, ETR and qP rate of inmutant leaves increased greatly compared with wild type. The result shows that photochemicalefficiency is not the key factor leading to decrease of net photosynthetic capacity in mutant, comparedwith wild type. The decline of CO2utilization efficiency, activity increase of the false loopphotosynthetic electronic pavement and the accumulation of ROS produced in false loop photosyntheticelectronic pavement are the key factor leading to the decrease of photosynthetic ability in the mutant.4. Genetic analysis indicated that the lm mutant is controlled by a single recessive gene. Usingmap-base clone we cloned the LM gene on the short arm of chromosome12. Sequence analysis showedthat the gene has a transversion from C to A in the first nucleotide of the intron. Protein sequenceshowed that LM encodes a P450monooxygenase which is an essential enzyme involving in plantserotonin biosynthesis pathway.