Reddy, M. K. | bioRxiv Science

bioRxiv2021

Comparative kinetic analysis of ascorbate (Vitamin-C) recycling dehydroascorbate reductases from plant and human.

Ascorbate, a primary antioxidant, gets readily oxidized to dehydroascorbate (DHA). Hence, recycling by dehydroascorbate reductase (DHAR) enzymes is vital for protection from cellular oxidative stress in eukaryotes. However, a detailed kinetic analysis of plant DHARs and their human orthologs; chloride intracellular channels (HsCLICs) is lacking. We demonstrate that DHAR from stress adapted pearl millet Pennisetum glaucum (PgDHAR) shows the highest turnover rate whereas HsCLIC1, 3, and 4 reduce DHA, albeit at lower rates. We further show that the catalytic cysteine is susceptible to varying levels of oxidation, supported by crystal structures and mass-spectrometry analysis. The differences in kinetic parameters among plant and human DHA reductases corroborate with the levels of reactive oxygen species H2O2 encountered in their respective intracellular environment. Our findings may have broader implications in crop improvement using pearl millet DHAR, and anti-cancer therapeutics targeting Vitamin-C recycling capability of human CLICs.

biochemistry↗

bioRxiv2021

Coordinated overexpression of OsSUT1, OsSWEET11 and OsSWEET14 in rice impairs carbohydrate metabolism that has implications in plant growth, yield and susceptibility to Xanthomonas oryzae pv oryzae (Xoo)

Enhancing carbohydrate export to sink tissues is considered as a feasible approach for improving photosynthetic efficiency and crop yield. In Oryza sativa Sucrose Transporter OsSUT1 located in companion cells and Sugars Will Eventually be Exported Transporters (SWEETs); OsSWEET11 and OsSWEET14 present in phloem parenchyma mesophyll cell plasma membranes are involved in long distance sucrose transport. OsSWEET11 and OsSWEET14 also play important role in host-pathogen interaction of rice plants and Xanthomonas oryzae pv oryzae (Xoo) that causes bacterial leaf blight. Three genes, OsSUT1, OsSWEET11, and OsSWEET14 were overexpressed under the control of their native promoters in rice to modulate long distance sugar transport and disease resistance. The transgenics displayed several phenotypic aberrations such as reduced plant height and seed weight due to altered sucrose transport and metabolism. Lower sucrose transport rate in transgenics than the WT resulted in reduced sucrose, fructose and glucose and increased starch accumulation in their leaves at the end of dark period. Transcriptional analysis revealed a reduction in the expression of genes involved in sucrose synthesis pathway in transgenics. Normal growth and development of transgenic seedlings were restored in growth media supplemented with 3% sucrose demonstrating in planta sucrose limitation. Remarkably, transgenic lines had diminished susceptibility to Xoo than the WTs due to low sugar content in the leaves demonstrating that rice plants maintain an optimum level of SWEETs for proper plant growth and development, and upregulation of these SWEETs in rice mimicks Xoo attack impelling plants to reduce sugar content in the apoplasm to inhibit pathogen growth.

plant biology↗