Characterization and expression of prohibitin during the mexican bean weevil (Zabrotes subfasciatus, Boheman, 1833) larvae development

Highlights

• The Z. subfasciatus prohibitins ZsPHB1 and ZsPHB2 exhibit structural features characteristic of the SPFH protein superfamily.

• PHB1 is present in various tissues and structures of Z. subfasciatus during larvae development.

• The regulation of ZsPHBs occurs at the transcriptional and post-transcriptional levels.

• This is the first characterization of PHB in Z. subfasciatus.

Abstract

Prohibitin (PHB) is a highly conserved eukaryotic protein complex involved in multiple cellular processes. In insects, PHB has been identified as a potential target protein to insecticidal molecules acting as a receptor of PF2 insecticidal lectin in the midgut of Zabrotes subfasciatus larvae (bean pest) and Cry protein of Bacillus thuringiensis in Leptinotarsa decemlineata (Colorado potato beetle). This study aimed to characterize the structural features of Z. subfasciatus prohibitin (ZsPHB) by homology modeling and evaluate its expression and tissue localization at different stages of larval development both at the transcript and protein levels. The samples were collected from eggs and larvae of different developmental stages. The immunodetection of ZsPHB was done with anti-PHB1 and confirmed by LC-MS/MS analysis. Gene expression analysis of ZsPHB1 and ZsPHB2 was performed by RT-qPCR, and immunohistochemistry with FITC-labeled anti-PHB1. Results showed that ZsPHBs exhibit distinctive characteristics of the SPFH protein superfamily. The transcript levels suggest a coordinated expression of ZsPHB1 and ZsPHB2 genes, while ZsPHB1 was detected in soluble protein extracts depending on the stage of development. Histological examination showed ZsPHB1 is present in all larval tissues, with an intense fluorescence signal observed at the gut. These results suggest a physiologically important role of PHB during Z. subfasciatus development and show its regulation occurs at the transcriptional and post-transcriptional levels. This is the first characterization of PHB in Z. subfasciatus.

Introduction

Z. subfasciatus (Boheman, 1833), commonly known as the Mexican bean weevil, is one of the main pests of the common bean (Phaseolus vulgaris) that affect seeds during storage (Morales et al., 2018). Weevils lay the eggs on the seed coat and then larvae feed and grow inside, which results in serious affectations including hollow grains with reduced nutritional quality and loss of viability. The economic impact caused by this insect pest has been reported to reach up to 35% production loss (Rodriguez-Hernandez, 2001; Nava-Perez et al., 2010).

Several chemical control methods have been effectively tested against bruchids; however, the use of toxic pesticides in a product that is about to be consumed represents a high risk, both for humans and the environment, which has evidenced the need for viable strategies to control the bean weevil through less harmful options that improve food safety and are compatible with sustainable production systems (Valencia-Cataño, 2006; Nava-Perez et al., 2010; Grossi-de-Sá et al., 2015; Dastranj et al., 2016).

Legume seed lectins have been studied for their insecticidal potential (Lagarda-Diaz et al., 2017; Hamid et al., 2013; Lagarda-Diaz et al., 2009; Grossi-de-Sa et al., 2007; Macedo et al., 2007; Zhu-Salzman and Salzman, 2001) and have shown harmful effects for the development of pest insects at different developmental stages, either by increasing their mortality, delaying their emergence, and reducing their fertility (Lagarda-Diaz et al., 2017; Grossi-de-Sa et al., 2007; Macedo et al., 2007; Shukla et al., 2005; Melander et al., 2003; Zhu et al., 1996). However, the incorporation of insecticidal lectins into a feasible control system still requires a more comprehensive understanding of their specific mechanisms of action upon interaction with susceptible insects.

Studies of the possible insecticidal mechanisms of the ironwood PF2 lectin (Olneya tesota) found that PF2 recognizes several soluble and membrane proteins of the larvae middle intestine during Z. subfasciatus development (Lagarda-Diaz et al., 2012; Lagarda-Diaz et al., 2014; Lagarda-Diaz et al., 2016), which suggests these proteins could be potential targets mediating the lectin toxicity. One interesting protein recognized by PF2 is prohibitin (PHB), which belongs to a family of scaffold proteins associated with the membrane lipid microdomains with a highly conserved region known as the SPFH domain (Stomatin, Prohibitin, Flotillin, and HflK/C) (Tavernarakis et al., 1999). This family of proteins was among the most represented in the transcriptome of Z. subfasciatus larvae, in which unigenes coding for prohibitin 1 (ZsPHB1) and prohibitin 2 (ZsPHB2) were identified (Lagarda-Diaz et al., 2020).

In humans and other model organisms it has been demonstrated PHB1 and PHB2 are very evolutionarily conserved, have molecular masses of 32–37 kDa (Wang et al., 2002), and can be located in the mitochondria, nucleus, nucleolus, endoplasmic reticulum, and plasma membrane, as well as in macrophage phagosomes (Thuaud et al., 2013). These proteins have been associated with multiple functions and are one of the best examples of proteins that present clear and distinctive roles depending on their intercellular location (Bavelloni et al., 2015). For instance, PHB acts as an adapter molecule in membrane signaling, a scaffold protein in the mitochondria, and a transcriptional co-regulator in the nucleus (Ande et al., 2017).

The study in insects of PHB expression at the transcript and protein levels has been very limited. PHB is believed to have a vital function for insects' normal development, since it has been implicated in the regulation of cell proliferation and apoptosis, controlling processes such as development and senescence (Mishra et al., 2006; Lagarda-Diaz et al., 2016). Larval metabolism and progression from larva to pupa in Drosophila have been linked to the expression of the Cc gene, an ortholog of PHB (Eveleth and Marsh, 1986). In the silkworm, Bombyx mori, PHB is differentially expressed, depending on the insect developmental stage or type of tissue, which indicates PHBs play an important role in the development of the worm (Lv et al., 2012). The oriental fruit fly, Bactrocera dorsalis, when subjected to heat stress is also capable of increasing PHB expression (Wei et al., 2015), although the function PHB exerts under thermal stress remains unknown. In the midgut of the Riphicephalus microplus tick, PHB is a receptor for a protozoan (Rachinsky et al., 2008), while in Aedes aegypti and A. albopictus PHB is a receptor for dengue virus (Kuadkitkan et al., 2012). In Leptinotarsa decemlineata, the potato weevil, PHB is a receptor for the insecticidal protein Cry3Aa produced by Bacillus thuringiensis (Ochoa-Campuzano et al., 2013).

Given the relevance that PHB has shown in insects either mediating the progression of larvae development and as a receptor of pathogens or entomotoxic proteins, PHB could be a promising target candidate for the development of biological control strategies against pest weevils. Therefore, we aim to characterize the structural features of ZsPHB and study its expression patterns at the transcript and protein levels and its histological detection during larval development of Z. subfasciatus to increase the basic understanding of its function in non-model insects.