Interplay of phytohormones facilitate sorghum tolerance to aphids

Authors: GROVER, SAJJAN - University Of Nebraska; AGPAWA, EARL - University Of Nebraska; Sarath, Gautam; Sattler, Scott; LOUIS, JOE - University Of Nebraska

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2020
Publication Date: 10/15/2020
Citation: Grover, S., Agpawa, E., Sarath, G., Sattler, S.E., Louis, J. 2020. Interplay of phytohormones facilitate sorghum tolerance to aphids. Plant Molecular Biology. 104(3). https://doi.org/10.1007/s11103-020-01083-y.
DOI: https://doi.org/10.1007/s11103-020-01083-y

Interpretive Summary: Plant tolerance is the unique ability in which a plant can withstand or recover from damage caused by insect herbivory. Tolerance is considered as the most durable category of resistance because it does not apply a selection pressure on insects, and plants are able to compensate for damage arising from insect herbivory via endogenous physiological mechanisms. Finding these mechanisms has been challenging and have largely proven elusive. In this current study, using genetically related sorghum plants, and an emerging sorghum pest, the sugarcane aphid, it was first possible to document plant tolerance in one genotypically distinct sorghum line. Further investigations documented a causal relationship between the levels of specific plant hormones and their precursors to the tolerance response of sorghum to the aphid pest. Tolerant plants contained higher basal levels of stress-related and growth-related hormones relative to non-tolerant lines. Boosting knowledge on mechanisms underlying plant tolerance will hasten its assimilation in breeding or engineering insect-tolerant plants and integrated pest management.

Technical Abstract: Plant’s encounter with insect herbivores trigger defense signaling networks that fine-tune plant resistance to insect pests. Although it is well established that phytohormones contribute to antixenotic- and antibiotic-mediated resistance to insect pests, their role in conditioning plant tolerance, the most durable and promising category of host plant resistance, is largely unknown. Here, we screened sorghum (Sorghum bicolor) nested association mapping (NAM) founder lines to identify and characterize sorghum tolerance to sugarcane aphid (SCA; Melanaphis sacchari Zehntner), a relatively new and devastating pest of sorghum in the United States. Our results suggest that the sorghum genotype SC35, the aphid-tolerant line identified among the NAM population, displayed minimal plant biomass loss and a robust photosynthetic machinery, despite supporting higher aphid population. Phytohormone analysis revealed significantly higher basal levels of 12-oxo-phytodienoic acid, a precursor in the jasmonic acid biosynthesis pathway, in the sorghum SCA-tolerant genotype compared to the wild-type (RTx430) and susceptible (SC1345) sorghum plants. Aphid feeding induced salicylic acid (SA) accumulation, but it appeared as a generalized plant response to aphids in all sorghum genotypes. Conversely, basal levels of abscisic acid and aphid feeding induced cytokinins were accumulated in the SCA-tolerant sorghum genotype, and these hormones may contribute to an increased photosynthesis and plant growth. Our findings imply that the aphid-tolerant sorghum genotype tightly controls the relationship among phytohormones, as well as provide significant insight into the underlying mechanisms that contribute to plant tolerance to sap-sucking aphids.