Sec-delivered effector 1 (SDE1) from the huanglongbing (HLB)-associated bacterium ‘Candidatus Liberibacter asiaticus’ was previously characterized as an inhibitor of defense-related, papain-like cysteine proteases in vitro and in planta. Here, we investigated the contributions of SDE1 to HLB progression. We found that SDE1 expression in the model plant Arabidopsis thaliana caused severe yellowing in mature leaves, reminiscent of both ‘Ca. L. asiaticus’ infection symptoms and accelerated leaf senescence. Induction of senescence signatures was also observed in the SDE1-expressing A. thaliana lines. These signatures were apparent in older leaves but not in seedlings, suggesting an age-associated effect. Furthermore, independent lines of transgenic Citrus paradisi (L.) Macfadyen (Duncan grapefruit) that express SDE1 exhibited hypersusceptibility to ‘Ca. L. asiaticus’. Similar to A. thaliana, transgenic citrus expressing SDE1 showed altered expression of senescence-associated genes, but only after infection with ‘Ca. L. asiaticus’. These findings suggest that SDE1 is a virulence factor that contributes to HLB progression, likely by inducing premature or accelerated senescence in citrus. This work provides new insight into HLB pathogenesis.

Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

从黄龙病（HLB）相关细菌'亚洲假丝酵母（Candidatus Liberibacter asiaticus）'的Sec传递效应子1（SDE1）以前被表征为在体外和植物体内防御相关的木瓜蛋白酶样半胱氨酸蛋白酶的抑制剂。在这里，我们调查了SDE1对HLB进展的贡献。我们发现模型植物拟南芥中SDE1的表达在成熟叶片中引起严重的泛黄，使人联想到两个Ca。积雪草的感染症状和加速叶片衰老。在表达SDE1的拟南芥中也观察到衰老信号的诱导。线。这些特征在较老的叶子中明显，但在幼苗中不明显，表明与年龄相关的效应。此外，表达SDE1的独立的转基因柑桔（L.）Macfadyen（邓肯葡萄柚）品系表现出对Ca的高度敏感性。L. asiaticus'。与拟南芥相似，表达SDE1的转基因柑橘显示衰老相关基因的表达发生了改变，但仅在感染了Ca。L. asiaticus'。这些发现表明，SDE1是导致HLB进展的毒力因子，可能是通过诱导柑橘的过早或加速衰老而引起的。这项工作为HLB发病机理提供了新的见解。

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