The Role Of Auxin In The Process Of Foxtail Millet Panicle Infected By Sclerospora Graminicola

Sclerospora graminicola(Sacc.)Schroeter,the pathogen of Millet downy mildew,is an important oomycete disease that affects the yield and quality of foxtail millet.Infected foxtail millet will show various symptoms during the different stages.Among them,the early infection of S.graminicola will hinder the development and differentiation of panicle,resulting in no panicle,and the formation of "white tip" symptoms directly affect the yield of foxtail millet.In order to explore the main characteristics of the formation of "white tip" symptoms of foxtail millet and the process of S.graminicola infecting panical,field observation,determination of photosynthesis related indexes and microscopic observation of ears were carried out in different stages of foxtail millet with "white tip" symptoms;The differentially expressed genes and key regulatory factors in the formation of "white tip" symptoms were analyzed by transcriptome interaction;The mechanism of auxin in response to S.graminicola infection was determined by determination of auxin content,correlation analysis and parallel experiments.The main results are as follows:1.Through field investigation,determination of photosynthesis related indexes and microscopic observation of panicle,it was found that S.graminicola infected foxtail millet showed the phenomenon of internode shortening and plant height dwarfing.There was no difference in vegetative growth stage(S1)and growth cone extension stage(S2)between diseased panical and healthy panical;From panicle branch differentiation stage(S3)to the gynoecium and stamen formation stages(S5),the growth cones of diseased panical stopped developing,and the appearance became opaque and compact.At the later stage,the cells of the panical died.At this time,the hyphae of the pathogen had covered the whole cell space of the diseased panical and produced haustoria to invade the host mesophyll cells.The leaf area,photosynthesis and chlorophyll content of the second leaf of the diseased plant were significantly lower than those of the control.2.With the aid of RNA-seq technology,determine the difference in gene expression of grain panical infected by S.graminicola from the vegetative growth phase to the pistil and stamen differentiation phase(S1-S5).The analysis showed that a total of 17947 differentially expressed genes were screened in the S1-S5 period,of which the S4 and S5 periods had the largest number of differentially expressed genes,4484 and4692 respectively.Differentially expressed genes in the five periods were significantly enriched in GO pathways such as hormone-mediated signaling pathway,regulation of hormone levels,hormone metabolic process,and hormone biosynthetic process.KEGG was also significantly enriched in Tryptophan metabolism,Carotenoid biosynthesis,zeatin biosynthesis and other pathways related to hormone biosynthesis,among which tryptophan metabolism pathway is the most abundant.3.Using LC-MS/MS to detect the content of auxin hormones in the ears of 5 stages,a total of 5 types of auxin were detected: IAA,IAA-Glc,IPA,ICA,ICAld.These 5 types of auxin were found in diseased panical.The content of medium is higher than the control.The correlation analysis with the TPM expression of related genes in the transcriptome found that the expression of IAA biosynthetic pathways and the related regulatory genes of the transport pathway was up-regulated,and the expression of the IAA signal transduction pathway decreased.The results of the test showed that S.graminicola could induce the increase of IAA biosynthesis in the apical meristem of foxtail millet,but the IAA signal transduction pathway was blocked,causing the plants to show dwarf symptoms.4.In order to verify the role of IAA in the process of pathogen infection,by spraying IAA and IAA inhibitors,it was found that the formation rate of "white tip" in control area was 79.58%,and that of "white tip" in 50 mg / L IAA was 94.95%,which indicated that exogenous IAA could aggravate the infection degree of Foxtail Millet white hair disease,accelerate the mycelial expansion speed and produce more branches among host cells;spraying 50 μM / L NPA and 5 μM / L IAA could promote the growth of the host cells μM / L tannic acid could reduce the rate of white tip formation in infected foxtail millet,reduce and break the hyphal branches between host cells,and inhibit the formation of cystospores.