Revealing differential expression of phytohormones in sorghum in response to aphid attack using the metabolomics approach

Authors: HUANG, JIAN - OKLAHOMA STATE UNIVERSITY; SHRESTHA, KUMAR - OKLAHOMA STATE UNIVERSITY; Huang, Yinghua

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2022
Publication Date: 11/9/2022
Citation: Huang, J., Shrestha, K., Huang, Y. 2022. Revealing differential expression of phytohormones in sorghum in response to aphid attack using the metabolomics approach. International Journal of Molecular Sciences. 23. Article 13782. https://doi.org/10.3390/ijms232213782.
DOI: https://doi.org/10.3390/ijms232213782

Interpretive Summary: Sorghum, Sorghum bicolor (L) Moench, is the fifth most important cereal after rice, wheat, maize, and barley and cultivated worldwide. In the United States, grain sorghum is one of the most important dryland crops grown in the area stretching from Texas to South Dakota and expanding to other regions. Grain sorghum constitutes the main food grain for over 750 million people who live in the semi-arid tropics of Africa, Asia, and Latin America according to FAO statistics. Recently sugarcane aphid (SCA, Melanaphis sacchari Zehntner) has become a major insect pest on sorghum, causing severe damage to plants and significant yield loss. Thus, successful sorghum production is dependent upon the control of this devastating insect. Identification of natural resistance and use of genetically pest-resistant cultivars and hybrids in an integrated pest management program are the most economical and environmentally sound methods to reduce the negative economic impact of these damaging aphids. The main objective of this study was to assess the effect of phytohormones on host plant resistance to aphid attack. Two sorghum genotypes, BTx623 (susceptible) and Tx2783 (resistant), were selected for a comparative analysis of differential expression of a group of phytohormones between the two lines in responses to aphid infestation. The results generated from these experiments documented higher levels of the important plant hormones including jasmonic acid (JA), salicylic acid (SA), abscisic acid (ABA) and auxins in the resistant plant infested by SCA, indicating that aphid-induced upregulation of phtyhormone genes and exogenously applied hormones have important impact on sorghum plants to cope with aphid attack. Furthermore, molecular analysis (RT-PCR, real-time polymerase chain reaction) also showed that higher expression of phytohormones related marker genes in response to SCA feeding, providing a support to the early chemical analysis data. In summary, these findings provide new insight into a better understanding of the molecular mechanism of host plant defense against aphids and other phloem-sucking insects. The advanced understanding of the mechanisms underlying host palne resistance and the judicious use of resistant crop varieties will help protect sorghum crops from pest aphids through an effective pest management.

Technical Abstract: Sorghum (Sorghum bicolor) is an important multipurpose crop grown worldwide but like many other crops it is often threatened by insect pests. Sugarcane aphid (SCA, Melanaphis sacchari Zehntner ), for example, is one of the most severe pests in sorghum, which causes plant damage and yield loss. The main objective of this study was to assess the effect of phytohormones on host plant resistance to aphid attack. Two sorghum genotypes, BTx623 (susceptible) and Tx2783 (resistant), were selected for a comparative analysis of differential expression of a group of phytohormones in responses to aphid infestation. The quantification of phytohormones through LC-MS demonstrated higher levels of jasmonic acid (JA), salicylic acid (SA), abscisic acid (ABA) and auxins in the resistant genotype infested with SCA. The PCA plot supports the strong differential responses between resistant and susceptible genotypes; thus indicates the positive correlation between JA-ABA and negative correlation between SA-auxins. Similarly, RT-PCR results of the phytohormones-related marker genes showed higher expression in the resistant genotype compared to the susceptible one. Furthermore, to corroborate the role of phytohormones in plant defense, the susceptible genotype was treated with SA, JA and ABA. The exogenous application of SA and JA+ABA significantly reduced plant mortality, aphid number and damage in susceptible genotype, suggesting a strong correlation between phytohormones and plant survival. Our findings indicate that phytohormones play positive roles in plant defense against aphid and provide new insights into the molecular mechanisms operating in plants for self-protection. These findings would also stimulate further research into the mystery about the regulation of phytohormone production during plant interaction with aphids.