超表达OsPR1A增强了Xa21介导的水稻对白叶枯病的抗性反应

【背景】前期研究发现,水稻病程相关蛋白质OsPR1A的表达受上游抗病基因Xa21调控,接菌后早期启动Xa21介导的OsPR1A较高水平表达对水稻抵抗白叶枯病菌至关重要。同时OsPR1A也受到水稻白叶枯病菌（Xanthomonas oryzae pv. oryzae,Xoo）的诱导表达。对于OsPR1A的研究绝大部分是作为抗性反应发生的标志基因佐证其他基因或途径在抗性中的作用,缺乏直接的证据证实OsPR1A本身的生物学功能。【目的】通过获得OsPR1a-OX超表达转基因植株,调查其表型及农艺性状,并明确OsPR1A蛋白质表达与抗性的关系,为鉴定OsPR1A功能提供依据。【方法】通过农杆菌介导法,将构建的OsPR1a-OX转化载体转入到水稻受体4021中,利用PCR和免疫印迹（western blot,WB）技术分别在基因水平和蛋白质水平上筛选并鉴定OsPR1A超表达阳性纯合株系。在成熟期,调查OsPR1A超表达转基因植株的表型及农艺性状（株高、穗长、分蘖数、结实率和籽粒大小等）。在31℃条件下,将生长2周的水稻幼苗TP309、4021和OsPR1A超表达转基因植株接种水稻白叶枯病菌,并在接菌0、2、4、6、8、10和12 d时测量病斑长度。在接菌0、4和6 d时,收集TP309、4021和OsPR1A超表达转基因植株的水稻叶片,提取蛋白质,利用WB技术检测OsPR1A的表达特征。【结果】构建了OsPR1a-OX转化载体,并转入到受体4021中,筛选并鉴定到2个OsPR1A超表达转基因纯合株系（#704和#709）。调查了OsPR1A超表达转基因植株在成熟期的表型及农艺性状,与对照4021相比,#704和#709的株高较矮、穗长较短、分蘖数减少、结实率降低,但籽粒稍大,可能与结实率低有关。在31℃条件下,OsPR1A超表达转基因植株的病斑长度与对照4021相比明显缩短,结果具有显著性差异（P<0.05）。在接菌0、4和6 d的材料中,超表达转基因植株#704和#709中OsPR1A始终有较高水平的表达丰度,从而提高了对白叶枯病菌的抗性。【结论】采用农杆菌介导法,获得OsPR1A超表达转基因植株;超表达OsPR1A影响到水稻的正常发育过程;超表达OsPR1A后增强了Xa21介导的水稻对白叶枯病的抗性。

Overexpression of OsPR1A Enhanced Xa21-Mediated Resistance to Rice Bacterial Blight

【Background】Previous studies revealed that the expression of pathogenesis-related protein OsPR1A was regulated by the upstream resistance gene Xa21. The rapid induction of OsPR1A protein at early stage after inoculation was crucial in Xa21-mediated rice bacterial blight resistance. The expression of OsPR1A was induced by Xanthomonas oryzae pv. oryzae (Xoo). OsPR1A was well known as a marker gene to demonstrate the reaction between rice and pathogen, however, no direct evidence was obtained for the biological function of OsPR1A. 【Objective】 In this paper, transgenic plants overexpression OsPR1A were obtained and the phenotype and agronomic traits were investigated. The relationship between OsPR1A expression and resistance were surveyed to further explore the function of OsPR1A in the process of rice resistance to bacterial blight.【Method】The construct of OsPR1a-OX was transferred to rice recipient 4021 via Agrobacterium-mediated protocol. Positive homozygous transgenic lines were identified by PCR and western blot (WB) respectively. At the mature stage, the phenotype and agronomic traits of OsPR1A overexpression rice plants were investigated, including plant height, spike length, tiller number, seed setting rate and grain size. Rice seedlings of TP309, 4021 and OsPR1A overexpression plants grown for two weeks were inoculated with Xoo at 31℃. The length of lesions was measured at 0, 2, 4, 6, 8, 10, and 12 days post-inoculation (dpi) respectively. At 0, 4 and 6 dpi, the rice leaves of TP309, 4021 and OsPR1A overexpression plants were collected to extract total protein, and the expression profiling of OsPR1A were surveyed by WB.【Result】The OsPR1a-OX transformation vector was constructed and transformed into recipient 4021. Two homozygous OsPR1A overexpression lines (#704 and #709) were identified. At the mature stage, the phenotype and agronomic traits of the OsPR1A overexpression plants were investigated. Compared with the control 4021, #704 and #709 lines showed lower plant height, shorter panicle length, fewer tiller number, lower seed-setting rate. The grain size in transgenic rice plants were larger, which might be related to the lower seed-setting rate. At 31℃, the lesion length of OsPR1A overexpression plants was significantly shorter than that of the control 4021 (P<0.05). At 0, 4, and 6 dpi, the abundance of OsPR1A expression of overexpression plants was higher than that of 4021 and TP309, and the high level of OsPR1A protein might contribute to the resistance of Xoo.【Conclusion】OsPR1A overexpression transgenic plants were obtained by the Agrobacterium-mediated method. Overexpression of OsPR1A affected the normal development of rice plants and also enhanced the resistance to bacterial blight mediated by Xa21.