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Shriveled seed (svd), a P1B-type HMA5 transporter ATPase, is involved in copper detoxification to control sorghum growth and development

Tadesse, Dimiru Tilahun
The world population is projected to reach 9.6 billion by 2050, putting strong pressure on food security and agricultural productivity. Understanding plant developmental programs will aid in improving productivity by manipulating genetic pathways and identifying molecular markers that can be used in breeding programs for marker assisted selection. This project generally aims to examine environmentally regulated developmental mutants with the goal of identifying key developmental regulators that integrate environmental signals and understanding the mechanisms of their actions. Specifically, in this study I examined a heavy metal transporter and its impact on sorghum growth and development. Using a forward genetics approach employing a sorghum deletion mutant population, a total of 1,200 M2 fast neutron irradiated mutant lines were screened in the field to identify mutants. As a result, I found a severely affected developmental mutant named shriveled seeds (svd). The svd mutants display growth defects throughout development from germination to seed filling and appear to be particularly sensitive to heavy metals including copper and manganese. Whole genome sequencing and bioinformatics analysis showed there were seven deletions in svd mutant. One of these, the locus Sobic.006G173800, was found to cause the svd phenotype. Sequence analysis indicated that SVD encodes a heavy metal transporter P1B-type ATPase with 8 transmembrane domains, an ATP binding domain and metal binding domains. SVD is primarily localized in the cell membrane and based on the results from yeast 2 hybrid and BiFC analyses, SVD interacts with other metal binding proteins (metallochaperones) SbATX1 and SbFRN3 to extrude copper out of the cell. My gene expression study of svd mutants showed there are 951 differentially expressed genes including transporters, kinases, kinesins and histone related genes. A total of 38 genes were selected from the DEG genes based on the fold-change value and their co-expression level with SVD in Phytozome v13.0 for further analysis. This study was focused on understanding the mechanism of SVD function and its impact on sorghum development and maturation.