Gene Confers Resistance to HLB and Citrus Canker

Josh McGillHLB Management, International, Research

In August, Horticulture Research published a paper titled An endolysin gene from Candidatus Liberibacter asiaticus confers dual resistance to huanglongbing and citrus canker. Researchers found that an endolysin encoded by the Candidatus Liberibacter asiaticus (CLas) prophage has dual resistance to huanglongbing (HLB) and citrus canker. A prophage is the genetic material of a bacteriophage, and a bacteriophage is a virus that parasitizes a bacterium by infecting it and reproducing inside it.

HLB symptoms on citrus

In the study, two endolysin genes (LasLYS1 and LasLYS2) were cloned from the CLas genome. LasLYS2 had visible bactericidal activity against several rhizobium bacteria and Xanthomonas citri pv. citri (Xcc). More than two years of greenhouse testing confirm that LasLYS1 and LasLYS2 had durable resistance to HLB.

LasLYS2 transgenic plants do not show symptoms such as leaf chlorosis and root rot. LasLYS2 can completely clear CLas from infected plants. LasLYS2 transgenic plants with enhanced HLB resistance also exhibit resistance to citrus canker.

Ectopic expression of LasLYS1 and LasLYS2 in citrus promotes the proliferation of beneficial bacteria but inhibits the growth of Xanthomonadaceae and Rhizobiaceae in roots, which favors citrus defense response. Based on the structures of LasLYS1 and LasLYS2, researchers successfully synthesized four new endolysins with killing activity against CLas and Xcc.

The research provides insights for engineering bactericidal proteins or peptides against HLB and canker pathogens, as well as for breeding new citrus germplasm with broad-spectrum resistance. “The work shed light on the mechanisms of resistance of CLas-derived endolysins, providing insights for designing endolysins to develop broad-spectrum disease resistance in citrus,” the article’s abstract stated.

The article’s authors are Lanzhen Xu, Kaiqing Mo, Danlu Ran, Juanjuan Ma, Lehuan Zhang, Yijia Sun, Qin Long, Guojin Jiang, Xiaochun Zhao and Xiuping Zou. They are affiliated with the Citrus Research Institute, Southwest University/National Citrus Engineering Research Center in Chongqing, China.

Source: Nanjing Agricultural University/The Academy of Science

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