Dichotomous Role of Jasmonic Acid in Modulating Sorghum Defense against Aphids

Abstract

The precursors and derivatives of jasmonic acid (JA) contribute to plant protective immunity to insect attack. However, the role of JA in sorghum (Sorghum bicolor) defense against sugarcane aphid (SCA) (Melanaphis sacchari), which is considered a major threat to sorghum production, remains elusive. Sorghum SC265, previously identified as a SCA-resistant genotype among the sorghum nested association mapping founder lines, transiently increased JA at early stages of aphid feeding and deterred aphid settling. Monitoring of aphid feeding behavior using electropenetrography, a technique to unveil feeding process of piercing-sucking insects, revealed that SC265 plants restricted SCA feeding from the phloem sap. However, exogenous application of JA attenuated the resistant phenotype and promoted improved aphid feeding and colonization on SC265 plants. This was further confirmed with sorghum JA-deficient plants, in which JA deficiency promoted aphid settling, however, it also reduced aphid feeding from the phloem sap and curtailed SCA population. Exogenous application of JA caused enhanced feeding and aphid proliferation on JA-deficient plants, suggesting that JA promotes aphid growth and development. SCA feeding on JA-deficient plants altered the sugar metabolism and enhanced the levels of fructose and trehalose compared with wild-type plants. Furthermore, aphid artificial diet containing fructose and trehalose curtailed aphid growth and reproduction. Our findings underscore a previously unknown dichotomous role of JA, which may have opposing effects by deterring aphid settling during the early stage and enhancing aphid proliferative capacity during later stages of aphid colonization on sorghum plants.