Study On The Response To Salinity Change Of Kandelia Obovate At The Transcriptome Level Of Root Tissue

Mangroves are woody plant communities that grow in the coastal intertidal zone of tropical,subtropical regions,where an important feature of the habitat is high salinity and long-term exposure to seawater.Because of the peculiarities of the environment in which they live,they have developed a unique set of salt-tolerant mechanisms over a long evolutionary period that distinguish them from terrestrial and freshwater plants.Among them,Kandelia obovata is a common species of mangrove plants and is the most widely distributed mangrove plant in China.Therefore,this study uses K.obovata as the research object to explore its response mechanism under salt change.In the past,research on the salt response and tolerance mechanism of K.obovata has mostly focused on morphology and physiological and biochemical aspects,and research at the molecular level is still at an early stage.Therefore,this study starts from the transcriptome level and focuses on finding the key genes and key pathways of K.obovata to reveal salt response strategies.In addition,the study on salt-tolerance mechanism can also provide help for the introduction and artificial cultivation of it.The K.obovata seedlings are cultivated until the second pair of leaves had unfolded,then they are treated with three salinity environment(0‰,10‰,30‰)for 30 days.Root tissue samples are collected at three time points:before treatment(0 d),1-day after treatment,and 30-days after treatment,followed by physiological index determination,transcriptome sequencing,and bioinformatics data analyses.The main findings and conclusions of this study are as follows.1.The physiological indicators measured included chlorophyll fluorescence parameters F0,MDA content,proline content and SOD activity.After 1-day treatment at different salinities,compared with the control group(10‰ salinity group),the 0‰ salinity group had lower F0,lower MDA content in leaves,basically the same proline content in leaves,lower proline content in roots,lower SOD activity in leaves and higher SOD activity in roots.Compared with the control group,the 30‰ salinity group had lower F0(even lower than the 0‰ salinity group),higher MDA content in leaves,higher proline content in leaves,lower proline content in roots,basically the same level of SOD activity in leaves,and lower SOD activity in roots.2.Differentially expressed genes(DEGs)were screened with p-value<0.05 and |log2(fold change)|>1.The number of overlapping DEGs between groups is small and most of them are unique.After screening,a total of 585 DEGs were obtained between 30‰ salinity 1-day treated group and control group,with 208 up-regulated and 377 up-regulated.A total of 141 DEGs were obtained between 30‰salinity 30-day treated group and control group,with 87 up-regulated and 54 up-regulated.A total of 58 DEGs were obtained between 0‰ salinity 1-day treated group and control group,with 27 up-regulated and 31 up-regulated.A total of 288 DEGs were obtained between 0‰ salinity 30-day treated group and control group,with 145 up-regulated and 143 up-regulated.3.The DEGs and enriched metabolic pathways were significantly different in each treatment group.In the root tissues treated with 30‰ salinity for 1 day,the differences in nitrogen metabolism and flavonoid biosynthesis were observed.In the root tissues treated with 30‰ salinity for 30 days,the function of the differentially expressed genes was mainly to help the cells maintain homeostasis.Compared with the control group,the tissues treated with 0‰ salinity for 1 day showed little change,the different genes were significantly enriched in the PME(Pectin Methylesterase)and PLL(Pectinate Lyases)in the pectin degradation pathway,and the expression levels were decreased,and the pectin degradation process was weakened.In the root tissues treated with 0‰ salinity for 30 days,the function of the differentially expressed genes was mainly manifested as the enhancement of cell permeability and the enhancement of resistance to biological stress.Combining the results of all groups,it is speculated that K.obovata would first activate defensive measures when the salinity environment suddenly changed and then adjusted its metabolic activity according to the salinity of the outside environment.Compared to common salt response mechanisms in other plants,K.obovata has a set of more unique approaches:(1)under salt stress,the synthesis of suberin and lignin is increased,and the structure of cell wall is modified and changed to improve the ability of salt resistance and water retention.(2)in terms of signaling transduction,it may rely more on Ca2+as signaling molecules rather than on ABA.(3)due to its own metabolic pathway of tannin synthesis,K.obovata tends to use phenolic substances as the primary reactive oxygen scavengers.The salt response genes and pathways found in K.obovata can enrich the understanding of salt-tolerant mechanism of higher plants,provide more genetic resources for other plants' salt-tolerant gene engineering breeding and more theoretical guidance for the plantation of K.obovata,which has important practical significance.