Biological Function Of Ear Development Related Gene TaSPL20 From Wheat(Triticum Aestivum L.)

The common wheat(Triticum aestivum L.) is one of the most important food crops worldwide. Improving wheat yield has been the main objective of breeders. Wheat inflorescence and grain development are of vital importance to the formation of yield. Therefore, discovering genes involved in the development of inflorescence and grain and revealing their functional mechanism are valuable for understanding and improving grain yield in wheat. Squamosa-promoter binding protein-like genes(SPLs) encode plant-specific transcription factors. SPL genes are widely involved in processes of plant growth and development, morphogenesis and signal transduction. In the present study, we cloned Ta SPL20 s from three genomes of wheat based on the Ta SPL sequence, which was cloned previously by our group member and showed that specifically expressed in spike and apical meristem. Through a series of analyses, such as gene expression patterns in multi-tissue and development stages, association analysis and genetically modified rice, it was revealed that Ta SPL20 s could affect plant morphology and responds to inflorescence and grain development, finally affect the grain yield. The main research results are as follows:1. Ta SPL20-A, Ta SPL20-B and Ta SPL20-D were isolated from wheat genomes A, B and D, with the total fragment size 4690 bp, 2720 bp and 4740 bp, respectively. Using Chinese Spring nullisomic-tetrasomic lines, Ta SPL20-A, Ta SPL20-B and Ta SPL20-D were located on chromosome homologous group 7. Ta SPL20-A was mapped to a region flanked by molecular markers Xrz682-7A(8.41 c M) and Xfbb145-7A(4.09 c M) on chromosome 7A by a RIL population.2. Phytohormones play important roles in plant development. The responsive patterns of Ta SPL20-D to phytohormones were investigated in wheat seedlings. Ta SPL20-D underwent a significant decrease in the transcript level at the early stage of treatment by IAA, 6-BA and GA3, but Ta SPL20-D showed an opposite response to the treatment of GR24. Spatio-temporal expression analysis by q RT-PCR showed that Ta SPL20-D strongly expressed in lemma, palea and pistil of young ear. Deletion analyses on the Ta SPL20-D protein suggested that its variable C-terminal had transcriptional activation, but the N-terminal and SBP domain exhibited an inhibiting effect on its transcriptional activation.3. Polymorphism analysis showed that there were 8 and 2 polymorphic loci in Ta SPL20-A and Ta SPL20-D sequences respectively, which formed three haplotypes in each of these two genes. No polymorphic site was detected in the Ta SPL20-B sequence.4. Association analysis revealed that haplotype Hap3-A of Ta SPL20-A contributed to more total number of spikelet per spike in wheat. Ta SPL20-D haplotypes were significantly associated with 1,000-grain weight, number of spike per plant and plant height. The haplotype Hap1-D of Ta SPL20-D was considered as the favorable haplotype of increasing 1,000-grain weight and reducing plant height. Frequency ditribution in wheat modern varieties showed that haplotypes of TaSPL20-A and TaSPL20-D were selected during the breeding process. The distribution range and proportions of haplotypes Hap1-A and Hap1-D in Chinese modern cultivars were significantly enlarged in the last few decades.5. The Ta SPL20-D was transfered into rice. Compared with the control plants, transgenic plants showed a significant increase in ear length, primary branch, secondary branch, panicle grain number, grain length, grain width, 1,000-grain weight and empty seed in all lines, a reduced plant height in some lines, but no significant change in grain yield per plant.