Soybean Hypocotyls Prevent Calonectria ilicicola Invasion by Multi-Layered Defenses.

Michie Kobayashi,Chang-Jie Jiang,Khin Thuzar Win

doi:10.3389/fpls.2021.813578

Abstract

In plants, many pathogens infect a specific set of host organs to cause disease, yet the underlying mechanisms remain unclear. Here, we show that inoculation of soybean plants with Calonectria ilicicola, the soil-borne causal agent of soybean red crown rot, caused typical disease symptoms of root rot and leaf chlorosis and necrosis. However, the pathogen DNA was only detected in the roots and stem (hypocotyl) base but not other aerial parts of the plants. As we observed vigorous fungal growth in all culture media made of extracts from roots, stems, and leaves, differences in key components including available nutrients did not determine organ-specific infection and reproduction by C. ilicicola. Furthermore, inoculation of stems both with and without a surface wound showed that the stems resisted C. ilicicola infection via both the pre- and post-invasion defense layers. Transcriptomic comparison of roots and stems using RNA-seq analysis further revealed that upon C. ilicicola inoculation, a greater expression of genes involved in stress response was induced in the plant stems, including receptor-like kinase, AP2/ERF, MYB, and WRKY. In addition, pathways related to amino acid metabolism were also more upregulated in the stems in response to C. ilicicola infection. These results suggest that soybean stems provide C. ilicicola resistance, at least in part, by activating an organ-specific defense response.

Highlights

It is estimated that a plant is exposed to an average of 100 or more potential pathogens in the natural environment (Agrios, 1997)
Calonectria ilicicola inoculation at seed sowing resulted in severe root rot during the early growth stages of soybean plants, 1http://systemsbiology.cau.edu.cn/agriGOv2/ 2https://david.ncifcrf.gov/home.jsp followed by the appearance of brown necrosis on the lower leaves and yellow chlorosis in the upper leaves (Figure 1)
In the case of the soybean–C. ilicicola interaction, it is tempting to speculate that fungal invasion is perceived by these receptors in aspartate, glutamate, glycine, serine, threonine, and arginine) in stems, and two items for two amino acids in the roots, respectively (Figure 5C). These results suggest that amino acid metabolism may play important roles in response to C. ilicicola in soybean plants

Summary

Introduction

It is estimated that a plant is exposed to an average of 100 or more potential pathogens in the natural environment (Agrios, 1997). Some of these pathogens can infect all or most organs of their host plants, while others are more limited and cause disease in only one or a few specific organs or tissues, a phenomenon known as organ-specific or structural specific infection (Lacaze and Joly, 2020). Pathogens of powdery mildew disease only infect the epidermis of leaves and green shoots (Lynne, 2016) It remains largely unknown why some pathogens can infect the entire plant while others are restricted to specific organs

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