Phenotypic Analysis And Map-based Cloning Of Short Root Mutant 14-2M-4 In Arabidopsis

The root system is essential underground organ for plants, which provides plant with water, mineral nutrition and anchors the plants into soil. Plant root system originates from root stem cells which reside in root stem cell niche.Root Stem Cell Niche(RSCN) contains root stem cells and quiescent center(QC). The cell to cell signaling between the QC and surrounding stem cells plays an important role in maintaining stem cell fate. Thus the stable structure and function of RSCN is required for normal root development.We screened an EMS-treated seed library and obtained a short root mutant named 14-2 M-4. We performed the phenotypic analysis and map-based cloning analysis on 14-2 M-4, the major results are presented as follows:1. 14-2 M-4 mutant shows reduced root meristem cells, increased lateral roots and abnormal floral organsSeedlings of 14-2 M-4 have root defects in the length and show reduced meristemic cells and increase of lateral roots. Adult mutant plants have abnormal floral organs and altered silique arrangements on the stem. These results indicate that the mutation affects both the aerial organ and root development.2. The expression of QC-specific marker genes and Cyclin B1;1 is suppressed in 14-2 M-4GUS histochemical assay shows that the expression of QC-specific marker Rop GEF7pro:GUS was reduced significantly in the mutant 14-2 M-4, the cell division marker Cyclin B1;1:GUS was also suppressed, suggesting that the maintenance of the root stem cell niche and the cell division activity of root meristem may be affected in the mutant.3. The expression of root-stem-cell-determinant genes PLT1 and PLT2 was repressedThe expression of PLT1 and PLT2 in 14-2 M-4 mutant is repressed significantly, while the expression of SHR and SCR is not affected. Theses results indicate that the mutation in 14-2 M-4 may affect the maintenance of the root stem cell niche through PLT signaling pathway.4. The change in the polar location of PIN1 leads to abnormal auxin distribution in the root tip of 14-2 M-4The auxin efflux transporter PIN1 changed its localization from basal membrane to apical membrane of stele cells in 14-2 M-4. And the expression of DR5::GUS is decreased significantly in root tip. These data show that the mutation change the distribution of auxin in root tip through affecting the polarity of PIN1.5. The rough location of the mutation is determined by map-based cloning techniqueGenetic analysis shows the phenotype of 14-2 M-4 is caused by the recessive mutation of a single gene. Rough mapping was used to determine the mutation site of 14-2 M-4 being located around NT204 on the longer arm of chromosome 3. The fine mapping, was used to identify the mutation site being between MIG5-B and MRC8-B, the genetic distance is about 104 kb, which contain 29 genes.In summary, the mutation of 14-2 M-4 leads to defects in auxin-mediated root and aerial organ development. Based on our data, we speculated that this gene locus may play a vital role in the molecular network of auxin-regulated root development.