Bacterial blight of rice is caused by the γ-proteobacterium Xanthomonas oryzae pv. oryzae, which utilizes a group of type III TAL (transcription activator-like) effectors to induce host gene expression and condition host susceptibility. Five SWEET genes are functionally redundant to support bacterial disease, but only two were experimentally proven targets of natural TAL effectors. Here, we report the identification of the sucrose transporter gene OsSWEET13 as the disease-susceptibility gene for PthXo2 and the existence of cryptic recessive resistance to PthXo2-dependent X. oryzae pv. oryzae due to promoter variations of OsSWEET13 in japonica rice. PthXo2-containing strains induce OsSWEET13 in indica rice IR24 due to the presence of an unpredicted and undescribed effector binding site not present in the alleles in japonica rice Nipponbare and Kitaake. The specificity of effector-associated gene induction and disease susceptibility is attributable to a single nucleotide polymorphism (SNP), which is also found in a polymorphic allele of OsSWEET13 known as the recessive resistance gene xa25 from the rice cultivar Minghui 63. The mutation of OsSWEET13 with CRISPR/Cas9 technology further corroborates the requirement of OsSWEET13 expression for the state of PthXo2-dependent disease susceptibility to X. oryzae pv. oryzae. Gene profiling of a collection of 104 strains revealed OsSWEET13 induction by 42 isolates of X. oryzae pv. oryzae. Heterologous expression of OsSWEET13 in Nicotiana benthamiana leaf cells elevates sucrose concentrations in the apoplasm. The results corroborate a model whereby X. oryzae pv. oryzae enhances the release of sucrose from host cells in order to exploit the host resources.
白葉枯病菌能引發(fā)水稻白葉枯病，它利用第III類TAL（類轉(zhuǎn)錄激活子）效應(yīng)子誘導(dǎo)寄主基因的表達(dá)，并使寄主形成易被感染的狀態(tài)。有5個(gè)SWEET基因存在功能冗余性，參與病原菌侵染，但是通過實(shí)驗(yàn)證明其中只有2個(gè)基因是TAL效應(yīng)子的靶基因。本文中，我們報(bào)道了蔗糖轉(zhuǎn)運(yùn)蛋白基因OsSWEET13能夠作為PthXo2作用的易感病基因，并由于粳稻中OsSWEET13啟動(dòng)子的變化，存在潛在的對(duì)PthXo2介導(dǎo)的白葉枯病的隱性抗性。在秈稻IR24中，由于存在未知的效應(yīng)子結(jié)合位點(diǎn)，包含PthXo2的菌株能夠誘導(dǎo)OsSWEET13表達(dá)，而在粳稻品種日本晴和Kitaake中的等位基因不存在這些位點(diǎn)。這些效應(yīng)子相關(guān)基因被誘導(dǎo)以及易感病性是由于一個(gè)單核苷酸多態(tài)性（SNP），這個(gè)SNP也在OsSWEET13的多態(tài)等位基因中被發(fā)現(xiàn)，即來自水稻栽培稻明恢63中的隱性抗性基因xa25。通過CRISPR/Cas9技術(shù)將OsSWEET13突變，進(jìn)一步證實(shí)PthXo2介導(dǎo)對(duì)白葉枯病菌的易感病性需要OsSWEET13的表達(dá)。對(duì)收集的104個(gè)菌株進(jìn)行基因分析，表明OsSWEET13受到其中42個(gè)白葉枯菌種的誘導(dǎo)。在煙草中異源表達(dá)OsSWEET13會(huì)提高質(zhì)外體中的蔗糖濃度。這些結(jié)果證實(shí)一個(gè)模型，即白葉枯病菌會(huì)促進(jìn)寄主細(xì)胞蔗糖的釋放，進(jìn)而吸取寄主的營(yíng)養(yǎng)物質(zhì)。