HSP40 gene family in pearl oyster Pinctada fucata martensii: Genome-Wide identification and function analysis

Highlights

• Putative HSP40 genes were identified from Pinctada fucata martensii.

• PmHSP40 genes are highly diverse in sequence, domain structure.

• PmHSP40 genes are diverse in temporal and spatial expression profile.

• One highly induced PmHSP40 in low-temperature (PmHSP40LT) was coned.

• PmHSP40LT was significantly induced at low temperature and high temperature.

Abstract

HSP40, also called DnaJ, functions as a molecular chaperone by binding to Hsp70 and plays critical roles in the growth, development, and response to heat stress. However, this gene family is rarely reported in pearl oyster. In this study, 31 putative HSP40 genes from Pinctada fucata martensii (PmHSP40) were identified through bioinformatics methods and classified into three groups according to the presence of the complete three domains (J, G/F zinc finger domain, and cysteine rich domain). Further analysis showed that the PmHSP40 genes are highly diverse in sequence, domain structure, and tissue and development expression profile, implying diversified functions. In addition, one highly induced PmHSP40 in low-temperature (PmHSP40LT) was cloned, and its function in temperature response was explored. PmHSP40LT has a full length of 1741 bp, containing 1059 bp ORF, 152 bp 5′UTR, and a 507 bp 3′UTR, and encodes 352 amino acids. PmHSP40LT expression was significantly induced at low (17 °C) and high temperature (32 °C) at 6 h, 1 d, and 3 d relative to the control group. Thus, PmHSP40LT possibly participates in response to high and low temperatures in pearl oyster. In conclusion, all these results provide a comprehensive basis for the further analysis of PmHSP40 function in pearl oysters.

Introduction

Heat shock proteins (HSPs), also known as heat stress proteins, are a family of proteins produced by cells in response to various stressful conditions, such as toxins, oxidative conditions, hypoxia, glucose deprivation, water deprivation, osmotic pressure, infection, and inflammation [[1], [2], [3], [4]]. The HSP was first discovered from Drosophila melanogaster subjected to heat stress [5] and subsequently demonstrated to be ubiquitously and evolutionarily conserved molecular chaperones that are present in all living organisms [2,6,7]. Based on their molecular weights and functions, HSPs can be classified into several families, including HSP100, HSP90, HSP70, HSP60, HSP40, and low molecular mass HSPs [8]. HSP40, also known as DnaJ protein or J-protein [9], generally consists of a J domain, which binds to HSP70. As the co-chaperone of HSP70, HSP40 is capable of tightly regulating ATP hydrolysis, which is necessary for many normal housekeeping and stress-related functions [10]. In addition to the J domain, many HSP40 proteins contain other conserved regions, which are critical to their functions. Based on the difference in these regions, HSP40 proteins can be categorized into three groups according to the differences in these regions. Type I proteins are similar to Escherichia coli HSP40 with the J domain, Gly/Phe-rich region (G/F domain), and cysteine-rich domain (CxxCxGxG). Type II proteins possess the J domain and Gly/Phe-rich region, but lack the cysteine repeats, and type III has the J domain alone [11].

To date, more than 40 HSP40 homologs have been identified in mammals [12]. However, few HSP40s have been studied in mollusks. So far, only three HSP40 homologs were cloned from mollusks [[13], [14], [15]]. The pearl oyster Pinctada fucata martensii is an important economic shellfish species and mainly cultured for marine pearl production in the southern provinces of China and Japan. P. f. martensii is a warm-water shellfish that has a weak endurance capacity to low and high temperatures, thus temperature is an important environmental factor for their distribution [16]. It have been well verified that HSP40 plays important roles in protecting other animals from injury due to extreme temperature [13,15,17]. In Pomacea canaliculata, HSP40 was identified to be up-regulated under low temperatures [13]. In P. f. martensii, one HSP40 was cloned and demonstrated to be induced under thermal, low salinity, and bacterial challenges [15]. Our previous research showed that HSP40 was highly induced in P. f. martensii cultured at low temperatures [16]. Thus, it is meaningful to study the role of HSP40 in the adaptation of P. f. martensii to temperature change.

To understand the function of HSP40 in P. f. martensii (PmHSP40), we performed comprehensive genomic annotation and transcriptomic analysis on a large subset of HSP40 in P. f. martensii. Furthermore, we cloned and characterized one HSP40 and analyzed its sequential expression after temperature changes to determine the role of HSP40 genes in temperature adaption. The results could contribute to our understanding of the evolution and function of PmHSP40 in detail.