Map-based Cloning Of LVD2 Controlling Leaf Vein Density In Rice

In plants,leaf vein system is a continuous network of vascular bundles that connect all major plant organs and it transports photosynthetic products and soil nutrients over long distances,and providing mechanical support to plants.Rice（Oryza sativa L.）,C3 plant,is one of the main food crops of humans.But rice biomass is much lower than C4 plants,such as corn（Zea mays L.）and sorghum（Sorghum bicolor L.）.The main reason is that the photosynthetic efficiency of C4 plants is stronger than that of C3plants.One of the key reasons is that the leaf vein density of C4 plants is higher than that of C3 plants.Therefore,we screened some mutants of leaf vein density from C3 rice to study the molecular mechanism of controlling leaf vein density.It can contribute to the creation of material with the C4-like leaf vein density.In this dissertation,one of the mutants with increased leaf vein density was used as the material and named lvd2（leaf vein density 2）.The main findings are as follows:1.There are 9 veins and 12 veins in the wild type and lvd2 flag leaf within 2 mm,respectively.And the leaf vein density of lvd2 increases significantly.Compared with the wild type,lvd2 shows slightly dwarfish,narrower leaves.In lvd2,the area of the small veins is increased and the number of mesophyll cells between the two small veins is reduced.2.Compared with the wild type,the plant height,1000-grain weight,seed setting rate,biomass and effective tiller number of lvd2 are decreased;Physiological indicators of photosynthesis,stomatal conductance,intercellular CO₂ concentration,and transpiration rate are all improved,but photosynthetic rate is reduced.3.Through the method of map-based cloning,three alleles of LVD2 were found,and these three mutants were named lvd2-1;lvd2-2;lvd2-3.And they have the same phenotype.In lvd2-1,the mutation of G to T on the 5th exon results in the corresponding amino acid changing from methionine to isoleucine;In lvd2-2,the deletion of single base A on the ninth exon leads to a frameshift mutation and early termination of protein translation;In lvd2-3,the mutation of T to C in the 12th exon results in the corresponding amino acid changing from serine to proline.All three mutations lead to inactivation of LVD2,confirming the function of LVD2 preliminarily.LVD2 encodes a cyclin-related protein that is highly conserved within Gramineae.