| The green revolution is attributed to the semi-dwarf wheat cultivars developed by interference either of the biosynthesis or signaling of plant growth hormone gibberellic acid (GA). GA-deprived plants have negative impact on seedling emergence and vigor, root biomass, coleoptile, and leaf width, hence, compromised ability of the plants to deal with various abiotic stresses. Mutations in ATP Binding Cassette (ABC) type B1, which regulates auxin transport, seems more promising in reducing the plant height as it exhibits no adverse effect on agronomic traits in maize and sorghum. The goal of this study was to characterize the ortholog of the maize ABCB1 gene in wheat. N-termini and linker regions of ABCB1 carried species-, family-, and group- specific conserved motifs, possibly responsible for the specific functions. The near-identical conserved motifs of nucleotide binding domains showed subtle amino acid changes that possibly favored ATP binding to the N-terminus. Presence of the similar predicted 3-D protein structures and auxin binding residues suggested the involvement of ABCB1 in auxin transport in all the studied species including bread wheat, similar to maize and Arabidopsis. The three homoeologous copies of ABCB1 in wheat were mapped near the centromere of short arm of group 7 chromosomes. All three homoeologous copies expressed differentially during different developmental stages. 7B copy has major role in flower development whereas in nodes and internodes, 7B and 7A were involved. The TaABCB1 silencing resulted in reduced plant height with reduction in lengths of all the internodes with maximum reduction upto 46% in the lower internode. RNAi analysis resulted in the reduction of gene expression upto 62% in the second generation. In the second part of my research, a mutant resource was developed in a pre-green revolution cultivar Indian. Systematic evaluation of the population over generations provided an accurate estimate of the mutant stability and epimutations in wheat. Only 29% of the mutations observed during M2 were stable in M3 whereas 87% of the M3 mutations were stable in M4. 42 out of total 85 height mutants were identified as stable that were supposed to carry mutations other than the known rht mutations. |
