Global Responses of Resistant and Susceptible Sorghum (Sorghum bicolor) to Sugarcane Aphid (Melanaphis sacchari)

Abstract

The sugarcane aphid ( Melanaphis sacchari ) has emerged as a significant pest for sorghum. The use of sugarcane aphid-resistant sorghum germplasm with integrated pest management strategies appears to be an excellent solution to this problem. In this study, a resistant line (RTx2783) and a susceptible line (A/BCK60) were used to characterize the differences in plant responses to the sugarcane aphid through a series of experiments, which examined global sorghum gene expression, aphid feeding behavior and inheritance of aphid resistance. The global transcriptomic responses to sugarcane aphids in resistant and susceptible plants were identified using RNA-seq and compared to the expression profiles of uninfested plants at 5, 10, and 15 days post-infestation. The expression of genes from several functional categories were altered in aphid-infested susceptible plants, which included genes related to cell wall modification, photosynthesis and phytohormone biosynthesis. In the resistant line, only 31 genes were differentially expressed in the infested plants relative to uninfested plants over the same timecourse. However, network analysis of these transcriptomes identified a co-expression module where the expression of multiple sugar and starch associated genes were repressed in infested resistant plants at 5 and 10 days. Several nucleotide-binding-site, leucine-rich repeat (NBS-LRR) and disease resistance genes similar to aphid resistance genes identified in other plants are identified in the current study which may be involved in sugarcane aphid resistance. The electrical penetration graph (EPG) results indicated that sugarcane aphid spent approximately twice as long in non-probing phase, and approximately a quarter of time in phloem ingestion phase on the resistant and F 1 plants compared to susceptible plant. Additionally, network analysis identified a phloem protein 2 gene expressed in both susceptible and resistant plants early (day 5) of infestation, which may contribute to defense against aphid feeding within sieve elements. The resistant line RTx2783 displayed both antixenosis and antibiosis modes of resistance based on EPG and choice bioassays between susceptible, resistant and F 1 plants. Aphid resistance from RTx2783 segregated as a single dominant locus in the F 2 generation, which will enable breeders to rapidly develop sugarcane aphid-resistant hybrids using RTx2783 as the male parent.

Variation Between Three Eragrostis tef Accessions in Defense Responses to Rhopalosiphum padi Aphid Infestation

“…The EPG results imply that the aphids settled and started probing more swiftly on the leaf of RTC-144 and spend less time non-probing than RTC-406. A recent study assessed the potential surface resistance of sorghum plants to sugarcane aphids ( Melanaphis sacchari ) and suggested that the aphids spend approximately twice longer in the non-probing phase in the resistant plants than in the susceptible plants ( Tetreault et al, 2019 ). Barley leaves infested with R. padi showed a shorter time of salivation and ingestion of the phloem on resistant relative to the susceptible plants.…”

“…Barley leaves infested with R. padi showed a shorter time of salivation and ingestion of the phloem on resistant relative to the susceptible plants. Feeding patterns reflect many factors, including mechanical barriers present at the leaf surface, olfactory repellents, and host metabolism ( Tetreault et al, 2019 ). The results highlight the need for conducting multiple bioassays combined with metabolic and transcriptomic methods to expose the mode of defense.…”

“…However, we found no significant difference between RTC-406 and RTC-144 in the phloem phase. Aphids are phloem feeders that occasionally feed on xylem fluid ( Nalam et al, 2020 ), possibly to attenuate the high osmotic potential of the phloem sap ( Douglas, 2006 ; Tetreault et al, 2019 ). The EPG results expose that aphids spent more time ingesting sap in the xylem on RTC-144 than RTC-406.…”

Pan-genome Analysis in Sorghum Highlights the Extent of Genomic Variation and Sugarcane Aphid Resistance Genes

“…In 2013, sugarcane aphid (SCA) emerged as a major insect pest of sorghum crops in North America (Alkan et al 2011). The line Tx2783 is highly resistant to SCA, and thus has great potential to boost breeding targeted at aphid resistance (Tetreault et al, 2019) ( Fig. 7B).…”

“…To investigate how gene expression is impacted by SCA, we remapped the RNA-Seq data before and after sugarcane aphid infestation from a previous study (Tetreault et al, 2019) to our Tx2783 genome. Gene expression analysis revealed that five out of the ten R genes expressed before and after SCA infestation ( Fig.…”