| Foxtail millet(Setaria italica(L.)P.Beauv.),which is an important minor crop,has the characteristics of drought tolerance and barren tolerance.Drought is a key factor restricting its growth,development and agricultural production.As a new plant hormone,strigolactones(SLs)plays an important role in crop stress resistance,but the mechanism of its effect on drought resistance of foxtail millet is still unclear.Yugu1(drought-tolerant)was employed in this study.The effects of exogenous strigolactones on physiological and biochemical responses to drought stress in foxtail millet seedlings were studied.At the same time,we employed Illumina sequencing technology to analyze the transcriptomes of the foxtail millet under control and exogenous strigolactones conditions,and the differentially expressed genes related to drought resistance were screened.The main research findings were as follows:1.The physiological and biochemical responses of foxtail millet seedlings under natural drought stress in field.Compared to the control group,the antioxidant enzyme activities,MDA content and proline content of the three varieties of foxtail millet seedlings were higher under drought stress,and the SOD activity,POD activity and MDA content reached a significant level.At the same time,the increase of SOD activity,POD activity and proline content of Yugu1 and Qinhuang2 were generally higher than that of An-04.There were dynamic changes in various indexes during the day,which generally showed a trend of earlier increasing and later decreasing.The chlorophyll content and photosynthetic physiological indicators of foxtail millet seedings was significantly reduced under drought stress.2.The effects of strigolactones on the seed germination characteristics of foxtail millet under drought stress.The seed germination rate,germination drought resistance index,relative radicle length and relative embryo length of foxtail millet showed a decreasing trend under drought stress.The seed germination rate and germination drought resistance index increased significantly under drought stress when exogenous strigolactones concentration was 10-8 mol/L~10-7 mol/L,while the effect of other concentrations was not obvious.Soaking seeds with different concentrations of exogenous strigolactones had an effect on seed relative radicle length and relative germ length under drought stress,but the difference was not significant.3.The influence of strigolactones on physiological characteristics in foxtail millet seedlings under drought stress.Compared with the control,SOD activity,POD activity,MDA content and proline content of foxtail millet leaves were significantly increased under PEG drought stress.SOD activity,POD activity and proline content were significantly increased under exogenous strigolactones treatment,while MDA content was significantly decreased;The activities of SOD,POD and the content of proline showed an increasing trend under the treatment of exogenous strigolactones and PEG drought stress,but did not reach the level under PEG drought stress.However,the content of MDA decreased,and was considerably lower than that under PEG drought stress.MDA content showed a trend of decline and was obviously lower than that under PEG drought stress.Compared with the control group,CO2 concentration(Ci),stomatal conductance(Cond),net transpiration rate(Tr)and net photosynthetic rate(Pn)of foxtail millet seedlings decreased significantly under PEG drought stress;CO2 concentration,stomatal conductance,net transpiration rate and net photosynthetic rate of seedlings showed a trend of increase under exogenous strigolactones treatment;CO2 concentration,stomatal conductance,net transpiration rate and net photosynthetic rate of foxtail millet seedlings showed a decreasing trend under the combined action of exogenous strigolactones and PEG drought stress,but all of them were significantly increased compared with PEG drought stress.4.Transcriptome analysis of strigolactones on foxtail millet seedlings.The transcriptome of foxtail millet seedings under exogenous strigolactones treatment was analysed by using high throughput sequencingtechnology.There were 1183 differentially expressed genes identified,of which 827 genes were up-regulated,356 genes were down-regulated,and 1151 genes were successfully annotated.There were many genes enriched in the metabolic pathways such as biosynthesis of amino acids,phenylalanine metabolism,glutathione metabolism,linoleic acid metabolism,alpha-linolenic acid metabolism and plant hormone signal transduction.And many proteins or transcription factors in these pathways were associated with the drought-resistant response process of plants.5.Expression characteristics of drought-resistant genes induced by strigolactones.There were 145 genes related to proline,antioxidant enzymes,chlorophyll,hormones and transcription factors screened from the metabolic pathways related to drought response.Through the analysis of the expression quantity of these genes by clustering heat map,we found that the most of genes were up-regulated and the differential expression multiple was larger,indicating that it was likely that the genes of foxtail millet seedings were significantly up-regulated after exogenous strigolactones treatment,so that the content of drought-related substances regulated by these genes was increased and the drought resistance of foxtail millet was enhanced.There were 17 genes related to drought resistance validated for real-time quantitative PCR.The results showed that their expression trends were consistent with the trend in the transcriptome results,and the correlation coefficient was 0.5332,indicating that the transcriptome sequencing data were reliable.In summary,the seed germination rate and the seeding physiological and biochemical functions of foxtail millet were seriously affected under drought stress,while exogenous strigolactones can improve the drought resistance of foxtail millet seedlings by enhancing osmotic regulatory substances(such as proline),improving the activity of SOD and POD,and reducing the damage of reactive oxygen species to cell membranes.At the same time,the high throughput sequencing technology was used to analyze the differential expression genes of foxtail millet seedlings under exogenous strigolactones treatment,and the genes related to drought resistance of foxtail millet were obtained,which can provide a theoretical reference basis for the research on the drought resistance mechanism of foxtail millet. |
PDF Full Text Request