| Tomato is a widely-grown vegetable crop worldwide.With China being a major producer and consumer of tomatoes and the development of facility agriculture,it is crucial to establish effective,green,and environmentally-friendly pest control strategies to maintain tomato production.Entomopathogenic fungi are a type of biological pesticide that is eco-friendly,however,the process of fungi directly infecting insects is hindered by various adverse environmental factors.As research progresses,it has been discovered that entomopathogenic fungi could be colonized in various host plants by means of leaf spraying,seed soaking,and root irrigation.The symbiotic relationship formed by entomopathogenic fungi and host plants could promote plant growth and induce the host plants to resist various pests and diseases.In this study,tomato and Beauveria bassiana;were used as research objects to explore the colonization process,duration and change of bacterial content of tomato colonized by B.bassiana in the ’B.bassiana-tomato ’symbiotic system.The effects of B.bassiana colonization on endogenous hormones signal transduction pathway in tomato were determined by screening transcriptome data and q PCR analysis.Finally,the effects of B.bassiana on the endogenous hormones of tomato were evaluated by the growth potential of tomato,the resistance to harmful organisms and the detection of tomato hormone content.These evaluations provide significant theoretical support for scientific and reasonable use of fungi and lay a foundation for further study of the interaction between B.bassiana and tomato.The main results of this study are as follows:1.The colonization process was observed by green fluorescent protein-labeled B.bassiana Bb252-gfp.In the observation of the colonization process,it was found that Bb252-gfp began to colonize the tomato leaves after 3 hours of leaf spraying and could be detected in adjacent stems and leaves.After 24 hours,Bb252-gfp was found to be present in almost all tomato tissues.Scanning electron microscopy showed that Bb252-gfp conidia penetrated into tomato leaf tissue through cell gaps at 12 hours,and gradually deepened at 24-48 h after colonization.After 72 hours,the germ tube of conidia could be observed.At 120 hours,the germinated spores adhered to a piece and grew further,but the germ tube failed to penetrate the tomato leaves to cause damage.At the same time,no conidia were observed to penetrate into the plant from the leaf stomata.The results of nested PCR showed that conidia could colonize in tomato plants for 35 d after entering tomato plants.By detecting the number of fluorescent single colonies by coating method and real-time fluorescence quantitative detection of B.bassiana specific bands,it was found that the bacterial content of tomato treated with Bb252-gfp was the highest at 7d,and the bacterial content decreased with the continuous colonization.2.According to the transcriptome data of tomato in the laboratory,5 plant endogenous hormone signal transduction pathways were screened,a total of 37 differential genes;a simple schematic diagram of these five plant endogenous hormone biosynthesis and signal transduction pathways was drawn.The q PCR of 37 genes showed that the IAA signal transduction pathway of tomato plants was activated at 14-21 d after Bb252-gfp treatment,which promoted plant growth and cell expansion.BR signal transduction pathway was activated at 14-28 d,which promoted plant cell elongation.The ETH signal transduction pathway was down-regulated in 35 d,and the growth restriction of tomato seedlings was relieved.The JA and SA signals were first up-regulated,then down-regulated,and finally up-regulated.The interaction between JA and SA makes the systemic induced resistance of tomato plants increase first,then decrease and then increase.3.In the experiment of measuring the growth potential of tomato plants after Bb252-gfp treatment,the growth of tomato plant height was promoted at 14-35 d,the leaf area increased rapidly at 7-21 d,and the plant dry weight increased continuously during the colonization of Bb252-gfp.After Bb252-gfp treatment of tomato plants,the oviposition of Bemisia tabaci was affected in a short period of time.The oviposition of B.tabaci was lower than that of the control group at 7 d,and the oviposition of B.tabaci increased slowly at the subsequent 14 and 21 d,gradually higher than the control.The determination results of five hormones in tomato plants showed that the treatment of Bb252-gfp increased the IAA content of tomato plants at 14,21 and 35 d,and decreased at 7 and 28 d.BR content increased at 21 and 28 d,and decreased at 7,14 and 35 d.ETH content increased 14-35 d after treatment.The synergistic regulation of IAA,BR and ETH promoted the growth and photosynthetic product accumulation of tomato plants,while the contents of JA and SA increased at 7 d,then decreased,and returned to normal levels until 28-35 d.The plant defense response intensity induced by JA and SA was the highest at 7 d,then decreased,even lower than the normal level,and returned to normal at about28 d.In summary,after Bb252-gfp treated tomato plants,conidia entered the leaves through cell gaps and transferred to all parts of the plant at 24 h.Bb252-gfp could colonize in tomato for about 35 d,and regulate plant growth and defense by affecting the synthesis and signal transduction of endogenous hormones in tomato plants.In the short term,the defense ability of tomato plants was significantly enhanced,then decreased,and finally slowly returned to normal.At the same time,the growth of tomato plants was significantly promoted.The above results provide a basis for further elucidating the interaction mechanism between entomopathogenic fungi and host plants,and provide a theoretical basis for better scientific and rational use of bacteria. |
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