4.3 Pathogen infection related gene families contracted inF. chinensis
Some of the contracted gene families in F. chinensis are associated with pathogen infection. Most of the contracted gene families involving in these pathways encoded actin-like protein. The actin protein is a fundamental component of the host cellular cytoskeleton, playing an important role in viral replication (Roberts & Baines, 2011; Spear & Wu, 2014). Previous research suggests that the actin gene is upregulated in M. japonicus after infection with Vibrio parahaemolyticus and WSSV (Ren, Zhang, Liu, & Li, 2019), the pathogens that cause the two most serious diseases affecting shrimp cultivation (Escobedo-Bonilla et al., 2008). The β-actin gene is also involved in WSSV infection in L. vannamei (J. Feng, Li, Liu, Tang, & Du, 2019). We speculate that the contraction of the actin gene family madeF. chinensis more sensitive to viral infections because the viruses could destroy the force-generating and macromolecular scaffolding properties of the actin cytoskeleton to drive the infection process (Spear & Wu, 2014). The lower number of actin genes may make it difficult to repair damaged cell in F. chinensis . This finding is consistent with those of previous studies, which indicate that F. chinensis exhibit lower resistance for WSSV than other shrimp species (Y. Feng et al., 2017; Jiang, Yu, & Zhou, 2006). This is one of the reasons why L. vannamei has replaced F. chinensis to become the dominant cultured shrimp species in recent years.
Higher temperatures often increase the severity of disease susceptibility (Cohen & Leach, 2020). Pathogen infection needs a suitable temperature, for example, the WSSV needs an optimum temperature to successfully enter the host hematopoietic stem cells, and the virus entry is blocked at 6 °C (Korkut, Noonin, & Soderhall, 2018).Fenneropenaeus chinensis is mostly distributed in the northern Pacific, a colder environment relative to that of other Penaeusspecies, where pathogen infectivity is weaker. We hypothesize that, during evolution, F. chinensis sacrificed an aspect of immunity to preserve more energy for subsistence in the cold environment, because immunoreaction is an energy-consuming activity (Alwarawrah, Kiernan, & MacIver, 2018; Hosomi & Kunisawa, 2020; Loftus & Finlay, 2016).