Roles Of Auxin Transcriptional Regulators In Phosphorus Uptake Via Arbuscular Mycorrhizal Fungi In Tomato Plants

Traditional agriculture methods use excessive fertilization to meet the demand of phosphorus for vegetables like tomato(Solanum lycopersicum L.),but low effective phosphorus utilization rate causes excessive accumulation of soil phosphorus,which has become one of the main obstacles to the development of sustainable agricultural production in China.Plant roots can symbiosis with arbuscular mycorrhizal fungi to effectively improve their absorption and utilization of phosphorus and other mineral elements in soil.Therefore,it is crucial to analyze the response mechanism of arbuscular mycorrhizal to low phosphorus stress on vegetable crops and improve their nutrient acquisition ability under adverse conditions by means of environmental regulation,physiology,biochemistry and molecular biology,to guarantee the yield and quality of vegetables and realize the sustainable development of agriculture in China.In this paper,roles of auxin response factor(ARFs)and auxin/indole acetic acid(Aux/IAA)on alleviating low phosphorus stress by arbuscular mycorrhizal fungi in tomato,were studied from gene expression,hormone level,biomass accumulation,plant phosphorus content and other aspects,by using tomato,an important horticultural crop,as experiment material and the technology of virus induced gene silencing(VIGS).The main results are as follows:1.Based on previous experiments,it was found that phyB mutation weakened phosphorus uptake via arbuscular mycorrhizal in tomato plants.We studied the effect of phytochrome B(phyB)on auxin content and its transcription regulators.It showed that the auxin content in the roots of phyB mutant materials was significantly lower than that of wild types.In addition,expression of ARF gene family in mutant materials was generally decreased,with the decrease of SIARF5 and SIARF9 being more significant and the up-regulation of SIARF6-I being obvious;however,expression of Aux/IAA gene family was generally increased with SlIAA9,SlIAA11 and SlIAA16 being significantly up-regulated.These suggested that phyB affected root auxin signaling pathway and its content accumulation,so as to further study the effect of auxin transcriptional regulatory factors on promotion of tomato phosphorus absorption via arbuscular mycorrhizal.2.We identified the role of different ARF genes in phosphorus uptake by arbuscular mycorrhizal.Silencing of SIARF6-1 gene will inhibit the expression of PT4 and PT5,the phosphorus transporter genes strongly induced by arbuscular mycorrhizal,so as to weaken the plant's phosphorus absorption capacity.Furthermore,the content of strigolactones(SLs)and the expression of CCD7,CCD8 andMAXl,which are related to its synthesis,were significantly decreased.On the contrary,after silencing SlARF5,phosphorus content and phosphorus concentration in silence plants was increased,and mycorrhizal colonization was significantly improved.The above results showed that SlARF6-1 and SIARF5,respectively,positively and neagatively regulated arbuscular mycorrhizal colonization,thereby alleviating or aggravating the response of tomato root system to low phosphorus stress.3.We investigated the effect of AuxlIAA genes on the phosphorous uptake by arbuscular mycorrhizal.When SlIAA9,SIIAAII,S1IAA16 silence,the content of SLs and its synthesis related genes CCD7,CCD8,MAXl expression decreased.Furthermore,the expression of PT4 and PT5,the key phosphorus transporters strongly induced by arbuscular mycorrhizal,were significantly reduced.Finally,the phosphorus absorption of plants was weakened and the dry matter accumulation was decreased,indicating that the auxin/indole acetic acid protein-encoding genes SlIAA9,SlIAA11 and SlIAA16 positively regulated the promotion of phosphorus absorption by arborescent mycorrhizal fungi.To sum up,studies have found thatARF and Aux/IAA genes of tomato regulate the hormone levels of SLs,affect the degree of arlbuscular mycorrhizal colonization,further regulate the expression of phosphorus transporter genes PT4 and PT5,and ultimately promote or inhibit the absorption of phosphorus and the accumulation of dry matter in tomatoes.The results of this paper can improve the utilization of soil phosphorus and realize the rational utilization of phosphorus resources in the future.