Small RNA Profiling Reveals Phosphorus Deficiency as a Contributing Factor in Symptom Expression for Citrus Huanglongbing Disease

Abstract

Huanglongbing (HLB) is a devastating citrus disease that is associated with bacteria of the genus 'Candidatus Liberibacter' (Ca. L.). Powerful diagnostic tools and management strategies are desired to control HLB. Host small RNAs (sRNA) play a vital role in regulating host responses to pathogen infection and are used as early diagnostic markers for many human diseases, including cancers. To determine whether citrus sRNAs regulate host responses to HLB, sRNAs were profiled from Citrus sinensis 10 and 14 weeks post grafting with Ca. L. asiaticus (Las)-positive or healthy tissue. Ten new microRNAs (miRNAs), 76 conserved miRNAs, and many small interfering RNAs (siRNAs) were discovered. Several miRNAs and siRNAs were highly induced by Las infection, and can be potentially developed into early diagnosis markers of HLB. miR399, which is induced by phosphorus starvation in other plant species, was induced specifically by infection of Las but not Spiroplasma citri that causes citrus stubborn-a disease with symptoms similar to HLB. We found a 35% reduction of phosphorus in Las-positive citrus trees compared to healthy trees. Applying phosphorus oxyanion solutions to HLB-positive sweet orange trees reduced HLB symptom severity and significantly improved fruit production during a 3-year field trial in south-west Florida. Our molecular, physiological, and field data suggest that phosphorus deficiency is linked to HLB disease symptomology.

Nutritional status of orange tree ‘Pêra Rio’ variety after Huanglongbing disease infection, leaf spray fertilization and application of resistance-inducing bioinductors

“…The re-establishment of the other nutrients supplied through leaves improves the ability of plants in the absorption and distribution of nutrient as long as new applications are carried out (Boaretto et al, 2003). These results are consistent with those mentioned by Zhao et al (2013) who found differences between healthy and diseased plants to the re-establish of the P content in plants with severe symptoms of HLB under leaf applications of phosphorus. The scenario of HLB control strategies is worrying.…”

Transgenic Plants That Express the Phytoplasma Effector SAP11 Show Altered Phosphate Starvation and Defense Responses

“…L. asiaticus), an intracellular bacterial pathogen, specifically induced microRNA 399 (miR399) in citrus plants (Zhao et al, 2013). MiR399 is induced by phosphate (Pi) starvation and has the ability to regulate the homeostasis of Pi by repressing the expression of PHOSPHATE2 (PHO2; Aung et al, 2006;Chiou et al, 2006).…”

“…L. asiaticus. The application of Pi reduces the disease symptoms of huanglongbing (Zhao et al, 2013).…”

Nucleotides, micro- and macro-nutrients, limonoids, flavonoids, and hydroxycinnamates composition in the phloem sap of sweet orange

“…Previous studies showed that CLasinfected citrus trees showed a 35% reduction in P compared to healthy trees. 38 The reduction of P in CLas-infected trees indicated that P could be required for the growth of CLas. In addition, genome analysis showed that the CLas encodes the znuABC genes responsible for the import of Zn.…”