Autophagy Regulates Whitefly-Symbiont Metabolic Interactions

Abstract

Nutritional symbionts are restricted to specialized host cells called bacteriocytes in various insect orders. These symbionts can provide essential nutrients to the host. However, the cellular mechanisms underlying the regulation of these insect–symbiont metabolic associations remain largely unclear. The whitefly, Bemisia tabaci MEAM1, hosts Portiera and Hamiltonella bacteria in the same bacteriocyte. In this study, the induction of autophagy by chemical treatment and gene silencing decreased symbiont titers, and essential amino acid (EAA) and B vitamin contents. In contrast, the repression of autophagy in bacteriocytes via Atg8 silencing increased symbiont titers, and amino acid and B vitamin contents. Furthermore, dietary supplementation with non-EAAs or B vitamins alleviated autophagy in whitefly bacteriocytes, elevated TOR (target of rapamycin) expression and increased symbiont titers. TOR silencing restored symbiont titers in whiteflies after dietary supplementation with B vitamins. These data suggest that Portiera and Hamiltonella evade autophagy of the whitefly bacteriocytes by activating the TOR pathway via providing essential nutrients. Taken together, we demonstrated that autophagy plays a critical role in regulating the metabolic interactions between the whitefly and two intracellular symbionts. Therefore, this study reveals that autophagy is an important cellular basis for bacteriocyte evolution and symbiosis persistence in whiteflies. The whitefly symbiosis unravels the interactions between cellular and metabolic functions of bacteriocytes. Importance Nutritional symbionts, which are restricted to specialized host cells called bacteriocytes, can provide essential nutrients for many hosts. However, the cellular mechanisms of regulation of animal–symbiont metabolic associations have been largely unexplored. Here, using the whitefly- Portiera / Hamiltonella endosymbiosis, we demonstrate autophagy regulates the symbiont titers, and thereby alters the essential amino acid and B vitamin contents. For persistence in the whitefly bacteriocytes, Portiera and Hamiltonella alleviate autophagy by activating the TOR (target of rapamycin) pathway through providing essential nutrients. Therefore, we demonstrate that autophagy plays a critical role in regulating the metabolic interactions between the whitefly and two intracellular symbionts. This study also provides insight into the cellular basis of bacteriocyte evolution and symbiosis persistence in the whitefly. The mechanisms underlying the role of autophagy in whitefly symbiosis could be widespread in many insect nutritional symbioses. These findings provide new avenue for whitefly control via regulating autophagy in the future.

Vitellogenin Facilitates Associations between the Whitefly and a Bacteriocyte Symbiont

“…Thus, the localization of Vg in the bacteriocyte is closer to that of Portiera than to Hamiltonella in the bacteriocyte. Additionally, Portiera is more ancient than Hamiltonella , so Portiera has a highly reduced genome and has lost its cell wall ( 36 , 56 , 57 ). The interactions between Vg and Portiera could facilitate the persistence of this symbiont in bacteriocytes.…”

“…dsRNAs specific to whitefly JHAMT (ds JHAMT ), whitefly Vg (ds Vg ), and GFP (ds GFP ) with sizes of 713 bp, 450 bp, and 420 bp, respectively, were synthesized using a T7 RiboMAX express RNAi system kit (Promega, USA), in accordance with the manufacturer’s instructions as described previously ( 13 , 34 , 45 , 47 , 57 , 61 ).…”

“…To study the effect of the JH pathway on Vg expression and Vg localization in whiteflies, approximately 800 female adult whiteflies at day 1 after emergence were injected with 1.5 μg/μL ds JHAMT and incubated on cotton leaf disks by using a previously described method ( 13 , 45 , 47 , 57 , 61 ). Control whiteflies were injected with 1.5 μg/μL ds GFP .…”

A novel microRNA regulates cooperation between symbiont and a laterally acquired gene in the regulation of pantothenate biosynthesis within Bemisia tabaci whiteflies

“…Progressive hypervacuolation, autophagy or apoptosis and transcriptional factors are involved in bacteriocyte development or death, which can control the changes in obligate symbiont populations, in the pea aphid Acyrthosiphon pisum (Simonet et al, 2018), the cereal weevils Sitophilus spp. (Vigneron et al, 2014), the seed bug Nysius plebeius (Matsuura et al, 2015) and whiteflies (Li et al, 2022; Wang et al, 2022). Because novel‐m0780‐5p agomir‐injection reduced the titre of Portiera in whiteflies, the miRNA could be used as another way for the host to control their symbiont population.…”

“…The miRNA antagomir is the chemically modified single‐stranded miRNA that complements the miRNAs and can specifically silence the endogenous miRNAs (Krutzfeldt et al, 2005). To investigate whether overexpression or repression of novel‐m0780‐5p influences PanBC localization in whiteflies, ~800 female adult whiteflies infected with Portiera within 3–4 days after emergence were injected with 3 µ m agomir or antagomir using an Eppendorf microinjection system following a previously described method (Bao et al, 2021; Li et al, 2022; Ren et al, 2021; Wang et al, 2022). The whiteflies that were injected with 3 µ m negative control agomir were used as a negative control for agomir injection.…”