Developmental transcriptomics reveals stage-specific immune gene expression profiles in Spodoptera frugiperda

Abstract

The fall armyworm, Spodoptera frugiperda, a globally invasive pest, demonstrates distinct immune adaptations across developmental stages and sexes, which are critical for its survival and adaptability. Using high-throughput RNA sequencing, this study systematically profiled 56 immune-related gene families, identifying 157 genes involved in Toll and Imd signaling pathways, and 185 genes associated with cellular immunity. Dynamic expression patterns were observed, with humoral immunity indices peaking during the third (L3) and fifth (L5) instars and diminishing in the pupal (P) and egg stages. In contrast, cellular immunity indices were highest in pupae and adult females, while the sixth instar (L6) and adult males exhibited the lowest immune capacity. Female adults displayed superior immune potential compared to males, reflecting evolutionary pressures tied to reproductive fitness. Notably, larval stages exhibited heightened immune gene expression, which aligns with their vulnerability to pathogens. Validation via qRT-PCR confirmed these transcriptomic trends, highlighting the modulation of immunity throughout development. These findings offer novel insights into the interplay between developmental progression and immune regulation in S. frugiperda. By elucidating these stage-specific immune responses, this study provides a robust framework for developing targeted pest management strategies aimed at mitigating the impact of this destructive pest.

Keywords: Spodoptera frugiperda; Cellular immunity; Development; Humoral immunity; Transcriptomics.

Fig. 1

Trends in the total gene expression of humoral and cellular immune index and their individual components index at different developmental stages in Spodoptera frugiperda. (A) Diagram of total humoral immune gene expression, recognition-related genes, Toll pathway-related genes, Imd pathway-related genes, effector genes, serine protease genes (SP), and serine protease inhibitors (SPI) in different developmental stages of S. frugiperda (the sum of Log2FPKM is used as the index calculation method). (B) Diagram of cellular immune gene expression index of S. frugiperda of developmental ages (the sum of Log2FPKM is used as the index calculation method). E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 2

Immune recognition-related gene expression profiles at different developmental stages of Spodoptera frugiperda. (A) Trends in total immune recognition gene expression (GNBPs and PGRPs) (the sum of Log2FPKM) at different developmental stages of S. frugiperda. (B) Heatmap of individual immune recognition gene expression profile (Log2FPKM) in humoral immunity at various developmental ages. E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 3

Toll pathway-related gene expression profiles at different developmental stages of Spodoptera frugiperda. The gene annotations and pathway mapping were based on KEGG (https://www.kegg.jp/entry/map04624). (A) Trends in total Toll pathway gene expression (the sum of Log2FPKM) at different developmental stages of S. frugiperda. (B) Heatmap of individual Toll pathway gene expression profiles (Log2FPKM) in humoral immunity at developmental ages. E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 4

Imd pathway-related gene expression profiles at different developmental stages of Spodoptera frugiperda. The gene annotations and pathway mapping were based on KEGG (https://www.kegg.jp/entry/map04624). (A) Trends in total Imd pathway gene expression (sum of Log2FPKM) at different stages of development of S. frugiperda. (B) Heatmap of individual Imd pathway gene expression profiles (Log2FPKM) in humoral immunity at developmental ages. E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 5

Effector gene expression profiles at different developmental stages of Spodoptera frugiperda. (A) Trends in total immune effector gene expression (sum of Log2FPKM) in S. frugiperda at different developmental stages. (B) Heatmap of individual effector gene expression profiles (Log2FPKM) in humoral immunity at developmental ages. E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 6

Serine proteases gene expression profiles at different developmental stages of Spodoptera frugiperda. (A) Trends in total immune serine protease gene expression (the sum of Log2FPKM) at different developmental stages of S. frugiperda. (B) Heatmap of individual serine protease gene expression profiles (Log2FPKM) at developmental ages. E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 7

Serine protease inhibitor gene expression profiles at different developmental stages of Spodoptera frugiperda. (A) Trends in total serine protease inhibitor gene expression (sum of Log2FPKM) in S. frugiperda at different developmental stages of S. frugiperda. (B) Heatmap of individual serine protease inhibitor gene expression profiles (Log2FPKM) in humoral immunity at various developmental stages. E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 8

Hemolymph coagulation-, clot formation-, and wound healing-related gene expression profiles at different developmental stages of Spodoptera frugiperda. (A) Trends in total immune hemolymph coagulation, clot formation, and wound healing gene expression (sum of Log2FPKM) at different developmental stages of S. frugiperda. (B) Heatmap of individual hemolymph coagulation, clot formation, and wound healing gene expression profiles (Log2FPKM) at various developmental stages. E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 9

Hematopoiesis-related gene expression profiles at different developmental stages of Spodoptera frugiperda. (A) Trends in total immune hematopoiesis gene expression (sum of Log2FPKM) at various developmental stages of S. frugiperda. (B) Heatmap of individual hematopoiesis gene expression profiles (Log2FPKM) in cellular immunity at various developmental ages. E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 10

Hemocyte-mediated immune response-related gene expression profiles at different developmental stages of Spodoptera frugiperda. (A) Trends in total hemocyte-mediated immune gene expression at different developmental stages of S. frugiperda. (B) Heatmap of individual hemocyte-mediated immune gene expression profiles (Log2FPKM) at various developmental ages. E: Egg; L1: 1st instar; L2: 2nd instar; L3: 3rd instar; L4: 4th instar; L5: 5th instar; L6: 6th instar; P: Pupa; AF: Adult female; AM: Adult male.

Fig. 11

RT-qPCR expression validation of immune-related genes in Spodoptera frugiperda. Expression levels of GNBP_Sfru123480 (A), PGRP_Sfru122870 (B), Toll_Sfru073570 (C), SPZ_Sfru073580 (D), DEF_Sfru018720 (E), Cec_Sfru063640 (F), AAMP_Sfru123110 (G), LP_Sfru056250 (H), dSR-CI_Sfru104410 (I), and Integrin_Sfru080300 (J) relative to the housekeeping gene (RpL32) by RNAseq and qRT-PCR across different developmental stages of S. frugiperda.