Regulation Of MiR408 On Photosynthetic Function Of Rice Leaves Under UV-B Stress

Rice?Oryza sativa L.?is not only one of the most important food crops in the world,but also one of the model plants used in research in the biological sciences.In recent years,with the rapid development of human society and the continuous advancement of industrialization,air pollution has become more and more serious,leading to the continuous reduction of the ozone layer,which has gradually increased the UV-B radiation reaching the surface,eventually leading to the reduction of production of rice and other crops.How to reduce the serious damage caused by UV-B to crops has become the focus of related research.miRNA are a type of endogenous non-coding small-segment single-stranded RNAs mainly found in eukaryotes.They are involved in the regulation of plant growth and development by responding to various stresses in a manner that is negatively regulated by target genes.Previous studies by the author's research team have shown that miR408 can respond to UV-B stress.However,when plants are subjected to enhanced UV-B stress,how miR408 and its target genes respond has not been studied.Therefore,this study utilized Nipponbare?WT?,miR408 overexpressing Nipponbare plant?M?,Zhonghua 11?WT1?and knockout target gene UCL8 in Zhonghua 11 plant?M1?as materials,and grow under natural light conditions as a control,and under the UV-B enhanced 40%irradiation,Nipponbare?BWT?,miR408 overexpressing Nipponbare plant?BM?,Zhonghua 11?BWT1?and knockout target gene UCL8 of Zhonghua 11 plant?BM1?as experimental materials.The author did the soil culture experiment.By using methods of physiology and biochemistry and molecular biology under these two conditions,the author studied miR408 and its target genes in rice response to enhanced UV-B stress for study on expression level and regulation mechanism of physiological and biochemical reactions.Concluded as follow:1.Compared with growth under normal light,both WT and miR408 overexpressing plants M showed a decrease in the number of tillers,shorter plants,and a significant decrease in yield and 100-grain weight after UV-B stress.Among them,the change of miR408overexpressing plants is more evident.It is speculated that miR408 overexpression can further decline the tolerance of rice to UV-B stress.From qRT-PCR analysis,the expression level of miR408 under UV-B radiation was significantly up-regulated.Under UV-B stress,the changes in agronomic traits such as plant height,tiller number,yield and 100-grain weight of rice knocked out UCL8 target genes were completely consistent with those of miR408overexpressing plants.It indicates that the UCL8 gene may be one of the target genes of miR408 in response to UV-B stress,and miR408 plays a negative regulatory role in UCL8.2.Under UV-B irradiation,the chlorophyll content of miR408 overexpressing plants BM and UCL8 knockout plants BM1 was more obvious than those of BWT and BWT1.After the analysis of chlorophyll biosynthesis metabolic intermediates,UV-B stress caused BM reduce chlorophyll content may be due to hindering from Urinary porphyrinogen III?UrogenIII?to Protoporphyrin IX?ProtoIX?during chlorophyll synthesis,which affects the photosynthesis.3.Compared with BWT,the BM of UV-B stress showed a significant decrease in stomatal conductance.It indicates that the degree of stomatal opening and closing of BM was affected by UV-B stress.Compared with BWT or BWT1,both BM and BM1 showed the significant decrease in net photosynthetic rate and water use efficiency,and the increase in intercellular carbon dioxide concentration.It indicates that UV-B inhibited the transport of CO₂ to mesophyll cells and reduced the utilization of water in leaf,thereby inhibiting the photosynthesis.It is speculated that UV-B stress further reduces the tolerance of plants to UV-B stress by inhibiting the photosynthetic efficiency of overexpressing miR408 plants.4.Under UV-B stress,the PSII energy flow and electron transfer of BM are damaged in great degree,and the increase of excess energy leads to the increase in heat dissipation,which leads to the decrease in photosynthesis performance.qRT-PCR analysis showed that the relative expression levels of BM and BM1 photosynthesis-related genes decreased significantly compared with BWT or BWT1 under UV-B stress.It shows that UV-B inhibits photosynthetic performance of miR408 overexpressing rice.The production of ROS is one of the main sources of reactive oxygen damage caused by abiotic stress.Under UV-B stress,the accumulation of H₂O₂ and MDA of BM was higher than those of BWT.It indicates that the balance of BM plant's antioxidant enzyme system was broken,the photosynthesis was inhibited,which results in worse growth of BM.It causes the decline of rice yield.