Transcriptome Analysis Of Kandelia Obovata And Avicennia Marina Leaves In Response To Submergent Hypoxia Stress

Flooding is one of the most widespread natural disasters.It is detrimental for nearly all terrestrial plants and results in growth reduction and ultimately death of many plant species.Mangroves are shrubs or woody trees lived in the costal intertidal zoon.They have many specific features to adapt to harsh conditions.Such as powerful above-root systems,aerenchyma and unique reproductive strategy-vivipary.Although physiology and morphology of mangroves adaptation to hypoxia were widely studied,the molecular mechanisms are still poorly understood.We applied transcriptome-wide RNA-seq technology to tackle molecular mechanisms of hypoxia in Kandelia obovata and Avicennia marina.For transcriptome analysis,leaves were collected at three different stages,short-term(0,4 and 12 h)and long-term(7 d)seawater immersion treatment,where simulating semidiurmal tides were performed with the inundation periods of 12 h and 4 h,respectively.Total RNAs were extracted from leaves of treated plants and RNA-seq libraries were constructed and sequenced.The main finding are:(1)Upon Gene Ontology(GO)and KEGG pathway annotation,in K.obovata and A.marina were mainly related to energy metabolism during submergencd and genetic information processing during flooding recovery.(2)The expression levels of genes related to energy and plant hormone metabolism in K.obovata and A.marina were analyzed.Through the analysis of anaerobic fermentation and trehalose metabolism,they were increased under the flooding conditions of K.obovata and A.marina.In the process of flooding recovery,the energy synthesis decreased.(3)By analyzing the synthesis and signal transduction of ethylene,abscisic acid and jasmonic acid,it was found that the genes involved in ethylene signal transduction were significantly up-regulated during flooding,including ETR,CTR,EBF and ERF,EIL.It was speculated that ethylene synthesis might increase rapidly and then decrease.In the recovery process,the expression of these genes was opposite.During abscisic acid synthesis,the gene encoding NCED rate-limiting enzyme was down-regulated,ABA8ox expression level was up-regulated,PYL expression level was up-regulated and PP2C expression level was down-regulated.Therefore,the content of abscisic acid decreases in flooding.However,the expression of ABA8ox,a key factor of abscisic acid catabolism,decreased during flooding recovery stage,and the downstream genes expression of abscisic acid is similar to flooding stage,so the content of abscisic acid may increase in flooding recovery.During flooding,the expression of PLA and KAT genes were up-regulated,and the expression of JMT was down-regulated,so the content of jasmonic acid increased during flooding.In the recovery process,the expression of KAT decreased,so the content of jasmonic acid might decrease in flooding recovery.(4)The ERF-VII genes of 4 different mangrove species were analyzed.The number of ERF-VII genes were different.The order is Sonneratia alba>A.marina>Rhizophora apiculata>K.obovata.No similar gene of AtHRE1 was found in these 4 mangrove species.These genes can be divided into 3 groups:RAP2.2/RAP2.12,RAP2.3 and HRE2.In this study,we analysed two mangroves adaption strateges from energy metabolism and plant hormones,providing a theoretical for the future study of mangrove adaptability mechanism.