| Plant growth promoting rhizosphere bacteria(PGPR)are bacteria parasitic on soil and plant roots,which can promote plant growth by directly stimulating plant growth or indirectly protecting plants from pathogens.PGPR affects the root growth and development of Arabidopsis thaliana by regulating the cell division and differentiation of primary roots and affecting the development of lateral roots.These effects lead to dramatic changes in root configuration,which significantly affect the growth of aboveground plants.However,the mechanism of different PGPR affecting plant root system is different.Herbaspirillum huttitense 5-28(hereinafter referred to as H.5-28)is a "interesting"bacterium isolated from the traditional Chinese medicine aconite by our laboratory.Previous studies showed that the strain could not only promote the root growth and biomass of some plants,including Arabidopsis thaliana,but also improve the disease resistance of Arabidopsis thaliana.The bacteria could be used a palnt growth promoting bacterium.The genomic information,physiological and biochemical characteristics of H.5-28 are obviously different from those of other PGPR.It means th at the mechanism of promoting plant root development and growth is different from that of other PGPR.In this study,the possible mechanism of H.5-28 promoting Arabidopsis thaliana root growth was explored.In this study,H.5-28 was inoculated into different plants to verify its growth-promoting effect,and the effect of H.5-28 on root growth of Arabidopsis thaliana was analyzed in detail.Different techniques,such as transcriptome,metabonomics qRT-PCR and LC-MS were used.The main results are as follows:1.H.5-28 can significantly increase the biomass and yield of several plants.Compared with the control,the biomass of corn,cucumber,tomato and Chinese cabbage increased by 1.08 times,2.00 times,1.19 times and 1.37 times,respectively,and the yield increased by 1.10 times,2.39 times,2.07 times and 1.16 times,respectively.Especially,compared to the control,the fresh weight,dry weight,root number and leaf area of Arabidopsis thaliana inoculated with H.5-28 were 8.10 times,3.33 times,4.86 times and 1.28 times,respectively.2.After Arabidopsis thaliana was treated with H.5-28,the expressions of plant hormone-related genes such as ethylene,jasmonic acid,salicylic acid,gibberellin,cytokinin and brassinolide in Arabidopsis thaliana changed significantly.Combined with the previous results that H.5-28 could significantly change the expression of genes related to phenylpropanoid biosynthesis,phenylalanine metabolism and plant hormone signal transduction,we speculate H.5-28 strain may affect plant hormone-related pathways,and then promote the root and cultivar growth of Arabidopsis thaliana.3.Using GC-MS technique,31 differential metabolites were screened from Arabidopsis thaliana inoculated with H.5-28.These differential metabolites were involved in sulfur metabolism,synthesis of more than 10 amino acids such as phenylalanine,and phenylpropane biosynthesis in Arabidopsis thaliana.The contents of abscisic acid(ABA),jasmonic acid(JA),gibberellin(GA3),zeatin(ZT)and salicylic acid(SA)in Arabidopsis thaliana inoculated with H.5-28 were significantly changed,indicating that H.5-28 could significantly affect the metabolism of endogenous plant hormones in Arabidopsis thaliana.The contents of ABA,GA3 and SA in Arabidopsis thaliana plants inoculated with H.5-28 were 18.76 times,3.44 times and 1.37 times,respectively,and the content of ZT was significantly increased,while the content of JA was 0.93 times.Further analysis showed that H.5-28 probably could affect Arabidopsis thaliana endogenous IAA metabolism,then affect the root growth,and last promot the plant growth.4.Compared with the control,the relative expression of TAA1,YUC1,YUC4,YUC6,YUC8 and YUC9 related to auxin synthesis in Arabidopsis thaliana treated with H.5-28 was 7.42 times,5.65 times,4.27 times,22.96 times,38.64 times and 9.21 times,and the relative expression of A UX1,LAX1,LAX2 and LAX3 related to auxin input was 2.67 times,2.89 times,1.82 times and 3.29 times,respectively.The relative expression of key genes PIN1 and PIN2 related to auxin output was 3.53 times and 11.22 times,and the relative expression of key genes ARF7,ARF19 and LBD18 related to auxin signal transduction was 4.24 times,4.23 times and 8.88 times.The results showed that H.5-28 could significantly increase the expression of genes related to synthesis,transport and signal transduction of endogenous IAA in Arabidopsis thaliana.LC-MS analysis showed that the content of IAA in Arabidopsis thaliana increased 8.39 times after inoculation with H.5-28.This may also be the main reason why H.5-28 affects the root growth of Arabidopsis thaliana and promotes the germination of lateral roots of Arabidopsis thaliana.It can be concluded that H.5-28 regulates plant auxin level,affects plant root development and promotes plant growth by affecting auxin synthesis,transport and signal transduction of endogenous IAA in plants.In summary,colonization of H.5-28 in Arabidopsis thaliana roots may affect phenylpropanoid biosynthesis at the transcriptional level,and then affect phenylalanine,tyrosine and tryptophan biosynthesis,thereby regulating tryptophan metabolism,stimulating and regulating Arabidopsis thaliana indolepyruvate pathway,promoting the synthesis,transport and signal transduction of endogenous auxins in Arabidopsis thaliana,promoting root growth in Arabidopsis thaliana,thus promoting the growth of Arabidopsis thaliana.In addition,H.5-28 could promote the growth of cucumber,corn,tomato and Chinese cabbage,and promote biomass and yield.Therefore,we speculate that H.5-28 has a broad-spectrum growth-promoting effect and has great potential to develop into biological bacterial fertilizer to improve plant quality and yield in the future. |
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