Three MYB Genes Coregulate The Phloem-Based Defence Against Engish Grain Aphid In Wheat

Aphids are typical phloem-feeding insects with a highly specialized mode of stylet penetration of plant vascular bundles.The stylet puncturing presents a unique stress on plant fitness and is often devastating to the production of agriculturally significant crops.As the most important food crop in numerous countries of the world,wheat is cultivated in many areas of the world.yield and quality of wheat are subject to serious impact with a variety of pest diseases,aphid feeding damage will bear the brunt.Aphids can feed on all aerial parts of wheat from Feekes stage 1,the development of the first leaf,through Feekes stage 11,grain ripening.Ubiquitous and continuous attacks cause constant damage to plant health,potentially inducing chlorosis and necrosis,repressing photosynthesis in the aerial organs,or directly destroying wheat grains,resulting in severe decrease of the grain yield.Aphids also transmit plant pathogenic viruses and phytoplasmas,severely impacting the quality and safety of the crop product.In response to pathogenic bacteria and aphid stylet puncturing of vascular bundles,plants defend themselves through the phloem-based defence(PBD)mechanism.PBD is produced under regulation by MYB transcription factors.Wheat PBD requires phloem lectins and may also require ?-1,3-glucan callose.The?-1,3-glucan callose,which is produced under catalysis by glucan synthase-like(GSL)enzymes and accumulates callose on sieve plates.Essential components of PBD include ?-1,3-glucan synthase-like proteins(GSL2,GSL10,and GSL12)and mannose-binding lectins Hfr-1 and Wci-1.MYB transcription factors can take part in multifarious regulations,in order to against biotic and abiotic stress.In the biological model plant Arabidopsis thaliana,15 of 37 tested MYBs are implicated in PBD against the green peach aphid(Myzus persicae L.).Up to now,full-length sequences of at least 73 TaMYB genes are known to exist However,most of them have not been characterized with definite roles in plant development or defence regulation.In fact,there is as yet no study showing the role of any TaMYB in wheat PBD against aphid.The effects of aphid infestations on expression levels of the 73 TaMYB genes were analysed.Eight TaMYB genes expression has increased by aphid induced,the most significant increased of expression level are TaMYB19,TaMYB29 and TaMYB44.A virus-induced posttranscriptional gene silencing(VIGS)technique was used to assess the effects of individual and combined MYB gene silencing on aphid feeding behaviours and wheat PBD responses.When the three MYB genes were independently silenced,aphid feeding on wheat phloem was facilitated and wheat PBD responses were repressed.TaMYB19,TaMYB29,and TaMYB44 were characterized as coregulators of wheat PBD against the insect.In the biological model plant,Ethylene mediated signaling pathway with MYB transcription factors crosstalk play an important role in the regulation of plant resistance to insects.EIN2 is an essential regulator of ethylene signalling and in plants under aphid attack it controls the expression of PP and GSL genes,leading to PP2 plugging and ?-1,3-callose closure of sieve pores along with callose coagulation on sieve plates.PP and callose are produced under regulation by ethylene signaling pathway.However,ethylene signaling pathway need MYB transcription factors.Plants were treated with ethylene signalling inhibitors AgNO3 and 1-MCP to elucidate whether ethylene signalling regulates the roles of TaMYB19,TaMYB29,and TaMYB44 in wheat PBD to English grain aphid.ethylene signalling inhibitors reduced expression levels of TaMYB,EIN2,PP and GSL.Therefore,TaMYB 19,TaMYB29,and TaMYB44 are coregulators of wheat PBD and execute this function by crosstalk with ethylene signalling.