Phenotypic Characterization And Gene Mapping Of A Rolled Leaf Mutant In Maize (Zea Mays L.)

Leaf shape is a key factor for ideal plant architecture breeding. Moderate leaf rolling maintains the erectness of leaves and minimizes the shadowing between leaves,which increases the photosynthesis of cultivars and hence raises grain yield. Leaf rolling plants avoid exposure to high irradiation by reducing transpiration rate and temperature of leaves under water deficit stress. Thus, leaf rolling is one of drought tolerance indexes. Recently, a series of genes regulating leaf development have been identified and cloned. Unearthing more leaf development related genes will lay vital foundations for ideal plant architecture breeding and basic theory research of crop leaf development.Recently we have found a rolled leaf Mutant by screening the maize mutant library generated from B73 and Mu active line hybridization. Adaxial leaf phenotype can be observed in the mutant elongation stage. The veins of swl leaf surface were twisty as leaf rolling of the mutant detected by SEM. The mutant has a performance of abaxial leaf which starts at the middle of leaf blade in the pot experiment. Anatomical analysis of the mutant was performed to find out what resulted in leaf curled inward morphology. Paraffin sections showed that the cell distribution of adaxial-abaxial was normal. The bulliform cell size was smaller in swl than in B73. However, there is no difference in cell number between swl and B73. We speculate that smaller bulliform cell might generate the leaf rolling.Seedling water deficit experiment showed that swl had a higher RWC and survival rate compared with B73, and this phenomenon had no relationship with stomata number. swl might improve its drought tolerance by reducing transpiration rate via leaf rolling.The genetic analysis indicated that the mutant trait was controlled by a single recessive gene. To map the target gene, F2 segregation population was construct using B73×swl. According to the BSR-seq technology, mutant pool and wild type pool derived from F2 population were used for RNA sequencing, and then swl gene was mapped in 165~185Mb interval on the chromosome 5. Based on BSR-seq data, we screened 13 pairs of SSR polymorphism markers between the parents around the 20 Mb interval. We later narrowed this interval using a small F2 population(N=78) with these 13 SSR markers, and then swl gene was mapped in 175-180 Mb interval on the chromosome 5 between SSR makers umc1822 and umc 1155. Larger genetic population was used for fine mapping the target gene. 2200 rolled leaf plants identified from F2 population were used to extract DNA and genotyped with SSR makers umc1822 and umc1155. 150 key recombinants were further analysised by Sequenom technology. Later we developed new SNP markers via PCR products sequencing method. Finally the candidate region was narrowed down to a 220 kb interval. Nine FGS(Filtered Gene Sets) were found in this region and each of them has not been studied. Relative gene expression experiment implied gene4 may be the causal gene as the lowest expression level. Seq-walking detected a Mu1 insertion in the promoter of gene4, which confirmed the expectation. These results provide useful and confident information for fine mapping and cloning swl gene in the future.