Characterization of physiological and molecular processes associated with potato response to Zebra chip disease

Chika C Nwugo,Li Tian,Hong Lin,Venkatesan G Sengoda

doi:10.1038/hortres.2017.69

Abstract

Transcriptional analyses identified molecular mechanisms associated with the response of leaf and root potato tissues to ‘Candidatus. Liberibacter solanacearum’ (Lso) infection, presumptive causal agent of zebra chip disease (ZC). Putative Lso infection affected several host processes including defense response-, regulation-, starch metabolism- and energy production-related processes. Interestingly, while proteinase inhibitors were strongly upregulated in leaf tissues, a concomitant downregulation was observed in root tissues. Quantitative polymerase chain reaction (qPCR) analysis suggests that alternative splicing might play a role. Furthermore, the transcriptional expression of redox homeostasis-related genes, including superoxide dismutase, showed the most inconsistent response to Lso in leaf and root tissues, highlighting potential targets of Lso susceptibility. Additionally, a net increase in gene expression in ZC-affected tissues despite the concomitant downregulation of photosynthesis-related processes, suggests a putative Lso-mediated low resource-use-efficiency. Subsequent nutritional analyses revealed a hypothesized Lso-mediated increase in nutrient accumulation, particularly a 210 and 108% increases in the potassium concentration of ZC-affected leaf and root tissues, respectively, suggesting an important role for potassium in ZC pathophysiology. This study highlights insights of above and below ground tissues in molecular and physiological aspects associated with potato response to ZC.

Highlights

Potato (Solanum tuberosum L.) is one of the most economically important non-grain crops
RNA-Seq analyses of leaf and root tissues of healthy and ZCdiseased potato plants yielded 13 606 125 read counts from healthy leaf tissues; 13 297 760 read counts from healthy root tissues; 15 907, 617 read counts from infected leaf tissues; and 16 772, 849 read counts from infected root tissues that matched to the potato genome sequence available in www.ncbi.nlm.nih.gov
Of the 34 genes tested in root tissues, 24 (71%) had a consistent pattern of expression with results obtained from RNASeq analyses, which included a proteinase inhibitor II gene that was shown to be strongly downregulated by both Quantitative polymerase chain reaction (qPCR) and RNA-Seq analyses (Figure 1b)

Summary

Introduction

Potato (Solanum tuberosum L.) is one of the most economically important non-grain crops. Zebra chip (ZC) is an emerging disease that affects all cultivated varieties of potato, resulting in significant revenue losses to commercial potato growers in the United States, Mexico, Central America and New Zealand.[1,2,3] ZC is associated with the psyllid Bactericera cockerelli (Šulc), which harbors ‘Candidatus Liberibacter solanacearum’ (Lso), a presumptive gram-negative phloem-limited α-proteobacterium.[1,4,5,6,7] Koch’s postulates have not been fulfilled due to the nonculturable attribute of Lso, there is a consensus agreement that Lso is etiologically associated with ZC.[1,6] Lso-infected potato plants routinely show ZC symptoms, such as leaf curling, leaf chlorosis, leaf scorching, starch accumulation in vines and dark striping of fried tuber slices.[8,9,10].

Methods

Results

Conclusion