Two venom allergen-like proteins, HaVAP1 and HaVAP2, are involved in the parasitism of Heterodera avenae.

Shujie Luo,Huan Peng,Shiming Liu,Lingan Kong,Wenkun Huang,Deliang Peng,Heng Jian

doi:10.1111/mpp.12768

Abstract

SummaryDespite the fact that venom allergen‐like proteins (VAPs) have been identified in many animal‐ and plant‐parasitic nematodes, studies on VAPs in Heterodera avenae, which is an important phytonematode, are still in their infancy. Here, we isolated, cloned and characterized two VAPs, named HaVAP1 and HaVAP2, from H. avenae. The two encoded proteins, HaVAP1 and HaVAP2, harbour an SCP‐like domain each, but share only 38% identity with each other. HaVAP1 and HaVAP2 are expressed in subventral and dorsal oesophageal glands, respectively. HaVAP1 is expressed mainly at the early stages, whereas HaVAP2 accumulates principally at the late stages. Both HaVAP1 and HaVAP2 are secreted when expressed in Nicotiana benthamiana leaves, but HaVAP1 is delivered into chloroplasts, whereas HaVAP2 is translocated to the nucleus without signal peptides. Knocking down HaVAP1 increased the virulence of H. avenae. In contrast, silencing of HaVAP2 hampered the parasitism of H. avenae. Both HaVAP1 and HaVAP2 suppressed the cell death induced by BAX in N. benthamiana leaves. Moreover, HaVAP2 physically interacted with a CYPRO4‐like protein (HvCLP) of Hordeum vulgare in the nucleus of the plant. It is reasonable to speculate that the changes in the transcript of HvCLP are associated with HaVAP2 during the parasitism of H. avenae. All results obtained in this study show that both HaVAP1 and HaVAP2 are involved in the parasitism of H. avenae, but they possess different functions, broadening our understanding of the parasitic mechanism of H. avenae.

Highlights

Phytonematodes, as well as other pathogens, are serious threats to plants worldwide
Two venom allergen-like proteins (VAPs) genes were cloned from H. avenae by rapid amplification of cDNA ends (RACE)
The CD-search from the National Center for Biotechnology Information (NCBI) identified a putative SCP-like extracellular protein domain which is located from peptide position 34 to 180 in HaVAP1 (Fig. S1b)

Summary

Introduction

The main differences between phytonematodes and other pathogens are that phytonematodes are animals and possess specific structures, such as stylets, amphids and secretory gland cells, for parasitism in plants (Baldwin et al, 2004; Davis et al, 2004). There are three general categories of effectors: first, cell wall-degrading enzymes (CWDEs), which loosen or degrade the cell wall for nematodes to pierce and colonize plants; second, metabolism-associated effectors, which induce the formation and maintenance of feeding sites for compatible interactions; and third, effectors that are used for the suppression of plant resistance responses (Ali et al, 2017). Most effectors are recognized as virulence proteins which promote compatible interactions with their hosts (Davis et al, 2008; Rosso et al, 2011)

Results

Discussion

Conclusion