The Tryptophan decarboxylase 1 Gene From Aegilops variabilis No.1 Regulate the Resistance Against Cereal Cyst Nematode by Altering the Downstream Secondary Metabolite Contents Rather Than Auxin Synthesis.

Qiulan Huang,Fang Chen,Hai Long,Guangbing Deng,Zhifen Pan,Minghui Zheng,Junjun Liang,Maoqun Yu,Haili Zhang,Lin Li,Qiao Li

doi:10.3389/fpls.2018.01297

Abstract

Cereal cyst nematode (CCN, Heterodera avenae) is a most important pathogen of wheat and causes tremendous yield loss annually over the world. Since the lack of resistance materials among wheat cultivars, identification and characterization of the resistance-related genes from the relatives of wheat is a necessary and efficient way. As a close relative of wheat with high resistance against CCN, Aegilops variabilis No.1 is believed to be a valuable source for wheat breeding against this devastating disease. However so far, very few resistance-associated genes have been characterized from this species. In this study, we present that the tryptophan decarboxylase genes from Ae. variabilis No.1 (AeVTDC1 and AeVTDC2) were both induced by CCN juveniles at the early stage of resistance response (30 h post-inoculation), with AeVTDC1 more sensitive to CCN infection than AeVTDC2. Silencing of AeVTDC1 led to compromised immunity to CCN with more CCN intrusion into roots; while overexpression AeVTDC1 in Nicotiana tabacum dramatically enhanced the resistance of plants by reducing the knots formed on roots. Metabolism analysis showed that the contents of secondary metabolites with activity of resistance to varied pathogens correlated with the expression level of AeVTDC1 in both Ae. variabilis No.1 and the transgenic tobacco plants. In addition, the content of IAA was not affected by either silencing or overexpressing of AeVTDC1. Hence, our research provided AeVTDC1 a valuable target that mediates resistance to CCN and root knot nematode (RKN, Meloidogyne naasi) without influencing the auxin biosynthesis.

Highlights

The cereal cyst nematode (CCN, Heterodera avenae) is a vital pathogen of graminaceous crops, such as wheat and barley
To determine which member of AeVTDC family mainly contribute to CCN resistance, expression pattern of AeVTDC1 and AeVTDC2 were tested and compared at 0 hour (h), 30 h, 3 day (d), 9 day post-inoculation of CCN
Expressions of AeVTDC2 were still higher but less than two times of that in control sample (Figure 1). These results indicated that expression of AeVTDC1 was much more sensitive to CCN infection than AeVTDC2

Summary

Introduction

The cereal cyst nematode (CCN, Heterodera avenae) is a vital pathogen of graminaceous crops, such as wheat and barley. Many efforts have been made to identify CCN resistance (Cre) genes. Gene resource resistant to CCN is scarce in wheat but abundant in its relatives (Montes et al, 2008). CreX and CreY were identified in Aegilops variabilis (Barloy et al, 2006). Ae. variabilis No. (2n = 4x = 28, UUSvSv), belonging to the genus Aegilops of the Triticeae tribe, is known as a well-resistant material, which confers strong resistance against CCN and root knot nematode (RKN, Meloidogyne naasi) (Barloy et al, 2006; Coriton et al, 2009; Xu et al, 2012; Zheng et al, 2015; Wu et al, 2016)

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Conclusion