Functional Divergence Of AOX1a From Populus Euphratica And P.pruinosa In Response To Abiotic Stresses

In higher plant,there are two respiratory pathways on mitochondrial membrane,cyanide-sensitive cytochrome C oxidase?COX?pathway and cyanide-insensitive alternative oxidase?AOX?pathway.Once plants are subjected to various stresses,the AOX pathway will be activated by alternative oxidases?AOXs?,which are located in the mitochondrial inner membrane and act as terminal oxidase in the mitochondrial electron transport chain.The AOX gene family is coded by a small gene family,and AOXs have been established as one of the essential defence components in the response of plant to biotic and abiotic stresses.In this study,we have isolated and identified AOX genes from P.euphratica and P.pruinosa respectively,and compared their functions divergence after diversification of the two desert poplars.The results were as follows:?1?The duplication of AOX genes in poplars.A total of four orthologus AOX genes were identified in genome of Populus euphratica and P.pruinosa respectively.Of them,AOX1a,AOX1b and AOX1c located on the chromosome 12 while AOX1d is located on chromosome 3that would attribute to one whole genome duplication event occurred in genome of Populus species.Whereas AOX1a,AOX1b and AOX1c were suggested duplicated by tandem duplications.The collinear analysis of the four genes confirmed this deduce,it was found that the duplication block of AOX1a,AOX1b and AOX1c had a collinear relationship with that of AOX1d,and the distance between AOX1a,AOX1b and AOX1c were less than 200kb on chromosome 12.?2?The over-expression of AOX1a from P.euphratica and P.pruinosa enhance proportion of cyanide-resistant respiration in total respiration.We investigated total respiration rate?V_t?,cytochrome c respiration rate(V_cyt)and cyanide-resistant respiration rate(V_alt)of the transgenic Arabidopsis lines,respectively.The results showed that there was no significant difference between Vt,V_cytyt and V_altlt except for that of in aox1a lines,but the ratio of V_cyt/V_t of aox1a was significantly higher than that of other lines,and the ratio of V_alt/V_t was significantly lower than that of other lines.However,in terms of V_cyt/V_t and V_alt/V_t,no significant difference were found between the WT and AOX over-expressed lines.These results suggested that over-expression of AOX could increase alternate respiratory activity to WT level.?3?The over-expression of AOX1a from P.euphratica and P.pruinosa improve Arabidopsis tolerance to abiotic stresses.Seed germination rate and root length of transgenic Arabidopsis lines with PeuAOX1a and PprAOX1a were tested with drought and salt treatments.The results showed that over-expression PeuAOX1a and PprAOX1a could increase the germination rate and root length after salt and drought stress.In terms of other physiological parameters,including MDA,MDA,EL,H₂O_2,proline and antioxidase activity.The results showed that Peu AOX1a and PprAOX1a significantly decreased the contents of MDA,EL and H₂O₂ in transgenic Arabidopsis.However,the content of proline and antioxidase activities,such as SOD and POD were increased,suggesting that over-expression of AOX1a reduced the damage of stresses to transgenic Arabidopsis.These results suggested that over-expression of PeuAOX1a and PprAOX1a genes in Arabidopsis could improve the tolerance of plant to salt and drought stresses.In conclusion,over-expression of AOX1a gene from P.euphratica and P.pruinosa could significantly improve plant tolerance to salt and drought stress by activating cyanide-resistant respiration,increasing antioxidase activities and reducing the accumulation of ROS?Reactive Oxygen Species?.Our results highlight the alternative pathway involved in the response of two desert poplars to stresses.