| Water shortage is a main problem in restrictting agriculture and becomes more and more obvious with the increase of world population,the water shortage of per capita and the uneven distribution of water resources.In the irreversible situation of water shortage,besides the use of water-saving irrigation methods,the role of biological water-saving in the development of water-saving agriculture has been paid more and more attention.Rice is one of the most important grain crops in China.The national rice production accounts for about 40%of the total grain yield and rice area accounts for about 28%of the total area of grain crops,while rice is also big agricultural water users.How to improve the water use efficiency of rice,research on water saving and drought resistance in rice,develop of water-saving rice,alleviate the contradiction between supply and demand of water resources,are of great significance in agricultural water saving and drought resistance.Phytochrome-interacting factors,which participate many growth and development processes and regulate including seed germination,hypocotyl elongation,chlorophyll biosynthesis,shade avoidance,circadian rhythm and etc,are the 15th subfamily of basic helix-loop-helix(bHLH)transcription factors.However,little is known about the role in drought stress.In our lab previously study,we found the ZmPIF1 and ZmPIF3 transgenic lines displayed enhanced tolerance to drought stress in rice,while the drought tolerant mechanism of ZMPIF1 and ZmPIF3 remains unclear.In this study,we investigate the the drought tolerance mechanism of PIFs in rice according to plant physiology,molecular biology,gene expression profiling and etc,preliminary analysis of the relationship between transcription factor ZmPIFl and ZmPIF3 with transpiration,stomata,ABA and the grain yield.1.Through water loss assay,measurement of transpiration rate and stomatal conductance,observation of stomata and etc,we compared the transpiration between ZmPIF1 and ZmPIF3 transgenic plants with wild type plants.The results suggested that the improved drought tolerance of ZmPIF1 and ZmPIF3 transgenic lines by reducing stomatal aperture and decreasing of transpiration rate,known as water saving and drought tolerance.2.To further clarify whether the reducing of stomatal aperture in ZmPIF1 and ZmPIF3 transgenic plants was associated with ABA,we investigated the ABA sensitivity of transgenic plants at the post germination stage and endogenous ABA level in the wild-type control and transgenic plants.We found the ZmPIF1 and ZmPIF3 transgenic lines were hypersensitive to exogenous ABA.However,the endogenous ABA level showed no significant change,which suggest ZmPIF1 and ZmPIF3 may be involved in ABA signalling pathway.3.We found that the expression level of drought stress related genes,stomatal apeature releated genes and ABA signalling pawthway related genes were significantly upregulated in ZmPIF1 and ZmPIF3 transgenic plants rather than wild type plants through comparing ZmPIF1 and ZmPIF3 transgenic plants digital gene expression with wild type plants.Moreover,expression level of ABA biosynthesis and catabolism related genes were found no significantly change in both ZmPIF1 and ZmPIF3 transgenic plants and wild type plants.These results were consistent with the result of endogenous level of ABA content,which further suggesting that ZmPIF1 and ZmPIF3 were involved in ABA signalling pathway by regulating stomatal opening and closing.4.To explore the drought tolerant molecular mechanisms of transcription factor ZmPIF1 and ZmPIF3 in rice,in this study we screened the rice cDNA library with the yeast two hybrid(Y2H)systems,and attempted to identify its interaction protein.MYB transcription factor family proteins,which were play important roles in the development and stress reponses of plants,were isolated as candidate for interaction protein.However,the interaction mechanisms of ZmPIF1 and ZmPIF3 with these proteins need to be futher clarified.5.In addition,we examined several agronomic traits of the ZmPIF1 and ZmPIF3 transgenic plants under normal conditions for two cultivating seasons(2015 and 2016).These results indicated that ZmPIFl and ZmPIF3 were able to increase tiller angle and grain yield contributed by improved panicles in transgenic rice.Overall,these results suggested that ZmPIF1 and ZMPIF3 play important role in ABA-mediated regulation of stomatal opening and colsing and decrease of transpiration,which significantly improve water-saving and drought tolerance of transgenic plants.ZmPIFl and ZmPIF3 transgenic plants also have good agronomic traits,demonstrating the efficacy of ZmPIF1 and ZmPIF3 in crop improvement. |
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