Abstract

BackgroundRoot parasitic weeds are a major constraint to crop production worldwide causing significant yearly losses in yield and economic value. These parasites cause their destruction by attaching to their hosts with a unique organ, the haustorium, that allows them to obtain the nutrients (sugars, amino acids, etc.) needed to complete their lifecycle. Parasitic weeds differ in their nutritional requirements and degree of host dependency and the differential expression of sugar transporters is likely to be a critical component in the parasite’s post-attachment survival.ResultsWe identified gene families encoding monosaccharide transporters (MSTs), sucrose transporters (SUTs), and SWEETs (Sugars Will Eventually be Exported Transporters) in three root-parasitic weeds differing in host dependency: Triphysaria versicolor (facultative hemiparasite), Phelipanche aegyptiaca (holoparasite), and Striga hermonthica (obligate hemiparasite). The phylogenetic relationship and differential expression profiles of these genes throughout parasite development were examined to uncover differences existing among parasites with different levels of host dependence. Differences in estimated gene numbers are found among the three parasites, and orthologs within the different sugar transporter gene families are found to be either conserved among the parasites in their expression profiles throughout development, or to display parasite-specific differences in developmentally-timed expression. For example, MST genes in the pGLT clade express most highly before host connection in Striga and Triphysaria but not Phelipanche, whereas genes in the MST ERD6-like clade are highly expressed in the post-connection growth stages of Phelipanche but highest in the germination and reproduction stages in Striga. Whether such differences reflect changes resulting from differential host dependence levels is not known.ConclusionsWhile it is tempting to speculate that differences in estimated gene numbers and expression profiles among members of MST, SUT and SWEET gene families in Phelipanche, Striga and Triphysaria reflect the parasites’ levels of host dependence, additional evidence that altered transporter gene expression is causative versus consequential is needed. Our findings identify potential targets for directed manipulation that will allow for a better understanding of the nutrient transport process and perhaps a means for controlling the devastating effects of these parasites on crop productivity.

Highlights

  • Root-parasitic weeds in the family Orobanchaceae are among the major constraints to crop production worldwide [1,2,3], causing losses in crop yield and economic value estimated to be in excess of several billion USD annually [2, 3]

  • The obligate hemiparasite S. hermonthica has the largest number of expressed Monosaccharide transporter (MST) representative genes, just slightly greater than that found in the facultative parasite T. versicolor

  • Phylogenetic analysis of sugar transporter gene families We examined the phylogenetic relationships of the various members of the MST, Sucrose transporter (SUT) and Sugars will eventually be exported transporters (SWEET) gene families within and among the parasitic species in order to determine whether similarities and differences in particular clades account for the observed variation in estimated gene numbers

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Summary

Introduction

Root-parasitic weeds in the family Orobanchaceae are among the major constraints to crop production worldwide [1,2,3], causing losses in crop yield and economic value estimated to be in excess of several billion USD annually [2, 3]. Once formed, the haustorium attaches to the host root, develops invasive tissues that transverse the host root cortex, and eventually establish connection with the host vascular system Coincident with this is the development of specialized cells and tissues that allow the parasite to obtain and utilize host derived nutrients [10]. Root parasitic weeds are a major constraint to crop production worldwide causing significant yearly losses in yield and economic value. These parasites cause their destruction by attaching to their hosts with a unique organ, the haustorium, that allows them to obtain the nutrients (sugars, amino acids, etc.) needed to complete their lifecycle. Parasitic weeds differ in their nutritional requirements and degree of host dependency and the differential expression of sugar transporters is likely to be a critical component in the parasite’s post-attachment survival

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