Pantothenate mediates the coordination of whitefly and symbiont fitness

Abstract

Intracellular symbionts in insects often have reduced genomes. Host acquisition of genes from bacteria is an important adaptation that supports symbionts. However, the function of horizontally transferred genes in insect symbiosis remains largely unclear. The primary symbiont Portiera housed in bacteriocytes lacks pantothenate synthesis genes: panB and panC, which is presumably complemented by a fused gene panB-panC (hereafter panBC) horizontally transferred from bacteria in Bemisia tabaci MEAM1. We found panBC in many laboratory cultures, and species of B. tabaci shares a common evolutionary origin. We demonstrated that complementation with whitefly panBC rescued E. coli pantothenate gene knockout mutants. Portiera elimination decreased the pantothenate level and PanBC abundance in bacteriocytes, and reduced whitefly survival and fecundity. Silencing PanBC decreased the Portiera titer, reduced the pantothenate level, and decreased whitefly survival and fecundity. Supplementation with pantothenate restored the symbiont titer, PanBC level, and fitness of RNAi whiteflies. These data suggest that pantothenate synthesis requires cooperation and coordination of whitefly PanBC expression and Portiera. This host–symbiont co-regulation was mediated by the pantothenate level. Our findings demonstrated that pantothenate production, by the cooperation of a horizontally acquired, fused bacteria gene and Portiera, facilitates the coordination of whitefly and symbiont fitness. Thus, this study extends our understanding on the basis of complex host–symbiont interactions.

Lysine provisioning by horizontally acquired genes promotes mutual dependence between whitefly and two intracellular symbionts

“…GQ332577) was maintained on cotton plants (Gossypium hirsutum cv. Shiyuan 321) as described previously [16,25,50]. The B. tabaci colony harbors Portiera, Hamiltonella, and Rickettsia [16,25].…”

“…Amino acid sequence alignments for each of the three genes were conducted using BioEdit v7.1.3.0 among the ten whitefly cryptic species including B. tabaci MEAM1, MED, MED-ASL, Asia I, Asia II-1, Asia II-3, Asia II-5, Asia II-6, SSA-ECA and New World (S1 Table ), Halmiltonella and Rickettsia. To construct the molecular phylogenetic tree for each of whitefly DapB, DapF, and LysA, a Bayesian inference (BI) analysis was conducted as described previously [9,50]. Protein sequences were aligned by MAFFT 7, trimmed by trimAL v1.3 with the -automated1 flag set for likelihood-based phylogenetic methods, and manually corrected in BioEdit v7.1.3.0.…”

“…DNA was extracted following the Nonidet-P40-based protocol as described previously [48]. Symbionts were quantified by qPCR using the CFX96 Real-Time PCR Detection System (Bio-Rad, Hercules, USA) with 2×SYBR Green master Mix (Bio-Rad) as described previously [16,25,50]. Portiera, Hamiltonella and Rickettsia were quantified using the copy number of 16S rRNA, 16S rRNA and gltA genes, respectively, with the B. tabaci β-actin gene as the internal standard for normalization.…”

“…To examine the metabolic function of horizontally transferred dapB, dapF, and lysA, E. coli lysine gene knockout mutants were generated and functional complementation with whitefly HTGs were carried out as described previously [16,50]. The E. coli K-12 BW25113 dapB, dapF and lysA knockout mutants (i.e., -ΔdapB, -ΔdapF, and -ΔlysA) were generated following the Lambda Red protocol as described previously [58][59][60].…”

“…Then E. coli wild-type K-12, mutant K-12, and mutant K-12 transformants with whitefly dapB, dapF or lysA were grown overnight in amino acid-deficient M9 minimal medium (Coolaber, Beijing, China) at 37˚C. The cell density of all the E. coli cells were measured at OD 600 using a microplate reader (Versa Max Molecular Devices, Silicon Valley, USA) as described previously [16,50]. Three biological replicates were conducted.…”