Contrasting amino acid profiles among permissive and non-permissive hosts of Candidatus Liberibacter asiaticus, putative causal agent of Huanglongbing

Abstract

Huanglongbing is a devastating disease of citrus. In this study, a comprehensive profile of phloem sap amino acids (AA) in four permissive host plants of Candidatus Liberibacter asiaticus (CLas) and three non-permissive Rutaceae plants was conducted to gain a better understanding of host factors that may promote or suppress the bacterium. The AA profiles of Diaphorina citri nymphs and adults were similarly analyzed. A total of 38 unique AAs were detected in phloem sap of the various plants and D. citri samples, with phloem sap of young shoots containing more AAs and at higher concentrations than their mature counterparts. All AAs detected in phloem sap of non-permissive plants were also present in CLas -permissive hosts plus additional AAs in the latter class of plants. However, the relative composition of 18 commonly shared AAs varied between CLas -permissive hosts and non-permissive plants. Multivariate analysis with a partial least square discriminant methodology revealed a total of 12 AAs as major factors affecting CLas host status, of which seven were positively related to CLas tolerance/resistance and five positively associated with CLas susceptibility. Most of the AAs positively associated with CLas susceptibility were predominantly of the glutamate family, notably stressed-induced AAs such as arginine, GABA and proline. In contrast, AAs positively correlated with CLas tolerance/resistance were mainly of the serine family. Further analysis revealed that whereas the relative proportions of AAs positively associated with CLas susceptibility did not vary with host developmental stages, those associated with CLas tolerance/resistance increased with flush shoot maturity. Significantly, the proline-to-glycine ratio was determined to be an important discriminating factor for CLas permissivity with higher values characteristic of CLas -permissive hosts. This ratio could be exploited as a biomarker in HLB-resistance breeding programs.

Mass spectrometry imaging as a potential technique for diagnostic of Huanglongbing disease using fast and simple sample preparation

“…SA and IAA are signaling compounds and may have a role in C Las as well as D. citri infection process in sweet oranges 57 . The increase of asparagine levels observed by DESI-MSI in Valencia oranges during the plant-pathogen interactions corroborates with literature 59 , 68 and was reported 66 as an abundant free amino acid (FAA) in permissive hosts that may be modulated by C Las.…”

“…The role of the amino acids isoleucine, valine, and tyrosine in the C Las infection process is not yet fully understood; however, it is known that C Las is incapable to produce such amino acids 78 . The same amino acids were detected in the flush shoots of Rutaceae host plants, flush shoots of D. citri nymphs 66 , and citrus leaves during defense responses to stress 45 .…”

Citrus vascular proteomics highlights the role of peroxidases and serine proteases during Huanglongbing disease progression

“…CLas has a reduced genome and synthesizes only six of the twenty proteinogenic amino acids de novo and must acquire the remaining amino acids from its surroundings (62). HLB susceptible Valencia sweet oranges are more abundant in amino acids like methionine and glutamate in comparison to HLB-tolerant genotypes including curry leaf, orange jasmine and trifoliate orange (63,64).…”

Size and shape analysis of Trioza erytreae Del Guercio (Hemiptera: Triozidae), vector of citrus huanglongbing disease

“…Traditional and geometric morphometrics have also been used for differentiation of psyllids collected from different geographic locations, or experiencing different chemical control programs or environmental rearing conditions . The effect of host plant species on the morphometric measurements of tomato/potato psyllid Bactericera cockerelli (Sulc) and ACP have been well documented with considerable variation, which could be attributed to the nutritional quality of the different host plant species, such as sugars and amino acids, that support survival and reproduction . However, it was also found that amino acids not obtained from phloem‐feeding may be produced by the symbiotic bacteria found in the psyllid, thus potentially ameliorating differences in nutrition levels provided from plants.…”