Identification Of A New Maize Dwarf Mutation Site And Its Function Analysis

Rational plant type is the morphological characteristics and reproductive basis of high-yield variety. Dwarfism is an important aspect of ideal plant type. Cultivating dwarf maize hybrids, can improve the structure of plants, increase planting density and improve group photosynthetic efficiency, thus to achieve the goal of high yield. Although more than100of maize plant height QTLs have been identified, few were cloned and applied to the genetic improvement. One maize plant height QTL-qphl has been identified by our study group, which was located at1.07bin chromosomes1. The confidence interval of qphl locates on the5th exon of maize Br2gene (Brachytic2/ZmPGPl); SNP5259cause an amino acid substitution from Arginine to Leucine and is proposed to be the functional site of qphl. The QTL caused moderate dwarf phenotype and exhibited great potential in breeding. This study is based on the previous studies, the QPH1gene identification and function analysis for further study and elucidated the molecular mechanism of plant height control. To further identify the functional site of SNP5259, we did back mutation of SNP5259and transformed to the Arabidopsis thaliana pgpl mutant and maize qph1mutant. These studies laid the theoretical basis of molecular mechanism of plant height growth and cultivation of suitable plant type. Results for these studies include:1. QPH1gene is a new allele of maize Br2gene, which encode a protein containing1379amino acids. The protein has two transmembrane domains and two nucleotide-binding domains. We cloned the1Kb promoter region of QPH1gene; sequence analysis showed that this region contained light response element and hormone response element.2. PromoterQPH1::GVS and Real-time PCR analysis indicated that QPH1gene express in root, stem and leaf, and there is no expression significant difference at different part between two maize lines. The protein encoded by the QPH1gene located in the cell membrane. The decreasing degree of auxin transport in qphl mutant is smaller than the br2null muatant.3. Site-directed mutagenasis by PCR, mqph1(mutagenized qphl) was transformed to the Arabidopsis thaliana pgpl mutant and maize qphl mutant.Over expression of mqph1can restore the plant height,hypocotyl length and auxin transport defect, and no difference between QPH1and mqphl transgenic plants. The transgenic maize exhibit stronger stem and higher plant height. The results confirm that SNP5259is the functional site of QTL-qphl.4. We found a different atpgpl muant from the mutants reported before, the mutant show shorter hypocotyls length and dwarfism phenotype. The distribution and content of auxin in root tip, and the NPA sensibility are different from the wild type. The relative auxin transport is lower than wild type. The mutant contained a T-DNA insertion in the third exon and was a null mutant, the muants used in the studies before may encode a truncated protein contained623amino acids.