Study On MADS-box Transcription Factor OsMADS25 In The Root Development And Salinity Stress Response In Rice

Rice is one of the important crops.Rice root system plays an important role in increasing the yield.The roots are exposed to various biotic and abiotic stresses for long time,and severe stress can cause a decrease in rice yield.Therefore,improving the root structure through genetic engineering,and then improving the adaptability to stress is an important way to improve rice yield.MADS-box is a family of transcription factors that widely exist in plants and their functions in plant root development and adaptation to stress still remain unclear.In this paper,the molecular mechanism by which OsMADS25 regulates the root development through auxin signaling pathway and improves tolerance to oxidative stress and salt stress through ABA-dependent signaling pathway and ROS scavenging pathway in rice was studied.The results are as follows:?1?The temporal and spatial differential expression patterns of OsMADS25 in rice tissues and organs and its responses to plant hormones and abiotic stress were analyzed.OsMADS25 was expressed at all stages and mainly expressed the roots.OsMADS25 was up-regulated by auxin,but inhibited by abscisic acid,and OsMADS25was also stimulated to express by external environmental signals such as NaCl,mannitol and polyethylene glycol.?2?OsMADS25 overexpression lines OsMADS25-OE and RNA interference lines OsMADS25-RNAi were used to study its roles in the root growth and development in rice.Compared to wild type,OsMADS25-OE lines exhibited promotion in the root system with increased primary root length,lateral root number,lateral root density and adventitious root length.but the opposite results were found in OsMADS25-RNAi lines.Under the condition of nitrogen-free nutrition,the root growth of OsMADS25-OE lines was also better than that of wild type.However,the root growth and development were significantly inhibited in OsMADS25-RNAi lines that showed poor adaptability to nitrogen deficiency.The effect of OsMADS25 on the growth and development of rice roots continued until the mature stage.Root rhizotron experiment showed that OsMADS25-OE lines had more developed root system in soil,while OsMADS25-RNAi had less root branches.?3?Auxin can rescue root growth and development defects caused by OsMADS25silencing.OsMADS25 was involved in the process of biosynthesis,transportation and degradation of auxin in rice.For one thing,overexpression of OsMADS25 can increase the content of auxin in rice roots.The polar transport?PAT?activity of OsMADS25-OE roots was significantly enhanced compared to that of wild type,whereas opposite results were found in OsMADS25-RNAi.Alternatively,OsMADS25 directly binds to the CArG motif in OsIAA14 promoter sequence,thereby regulating the auxin sigaling pathway in rice.OsIAA14 negatively regulates the auxin signaling pathway.OsIAA14 expression was up-regulated in OsMADS25-RNAi but down-regulated in OsMADS25-OE lines.?4?OsMADS25 transcript levels affected the accumulation of reactive oxygen species?ROS?in rice.Compared to wild type,overexpression of OsMADS25significantly reduced the accumulation of ROS in rice plants,including roots,shoots,mature leaves and bracts.Whereas,OsMADS25 silencing led to increased levels of ROS in rice plants.ROS are involved in the changes of epidermal cell growth in mature zone of rice primary root.Excessive accumulation of ROS led to reduced length of epidermal cell in the mature zone of primary root tip,thus inhibiting the growth and development of primary root.?5?Overexpression of OsMADS25 can improve the tolerance of rice to H₂O₂.OsMADS25 can regulate the expression of genes for ROS scavenging enzymes.OsGST4 encodes a glutathione S-transferase in rice,and its upstream promoter sequence contains a conserved sequence of CArG box,which can be directly bound by OsMADS25.Compared with wild type,the activity of glutathione S-transferase was significantly increased in OsMADS25-OE roots.Further study showed that osgst4 showed increased ROS accumulation,severe defects of growth and development,and enhanced sensitivity to salt stress and oxidative stress in rice.More importantly,the recombinant protein of OsGST4 has the ability to scavenge ROS in vitro.?6?Overexpression of OsMADS25 increased the salt tolerance in rice.Under the condition of glutamine as nitrogen source,there was no significant difference in root growth and development between wild type and OsMADS25 transgenic rice.When NaCl was added to the medium containing glutamine,overexpression of OsMADS25could increase the tolerance of rice roots to salt stress,while OsMADS25–RNAi lines showed a more sensitive phenotype.Under the condition of nitrate as nitrogen source,overexpression of OsMADS25 also increased the salt tolerance phenotype in rice.In addition,the germination rate of OsMADS25-OE seeds was also significantly higher than that of wild type under salt stress.?7?OsMADS25 regulates salt tolerance and oxidative stress tolerance in rice via ABA-dependent signaling pathway and ROS scavenging.Compared with wild type,OsMADS25-OE lines exhibited increased sensitivity to exogenous ABA,while OsMADS25-RNAi lines showed reduced sensitivity to exogenous ABA.ABA treatment led to the up-regulation of genes involved in stress dependent on ABA signaling pathway.ABA treatment promoted stomatal closure of rice leaves in OsMADS25-OE to improve adaptation to stress,and also changed the accumulation of ROS level in OsMADS25 transgenic rice roots.?8?After adding salt to the soil,the salt tolerance of OsMADS25-OE lines was significantly increased,and the chlorophyll content,proline content and soluble sugar content were significantly higher than those in wild type,while the opposite results were found in OsMADS25-RNAi lines.Under the condition of salt stress,the content of malondialdehyde?MDA?,which indicates the degree of cell damage,was significantly higher in OsMADS25-RNAi lines than that in wild type.OsMADS25 can directly bind to the promoter sequence of OsP5CR and activates its expression.OsP5CR encodes a pyrrolidine-5-carboxylic acid reductase which is a key enzyme in rice proline synthesis pathway.Expression of OsP5CR can increase the proline content and improve the adapt ability to stress in rice.