Expression Quantitative Trait Loci (eQTL) mapping for callose synthases in intergeneric hybrids of Citrus challenged with the bacteria Candidatus Liberibacter asiaticus

Abstract Citrus plants have been extremely affected by Huanglongbing (HLB) worldwide, causing economic losses. HLB disease causes disorders in citrus plants, leading to callose deposition in the phloem vessel sieve plates. Callose is synthesized by callose synthases, which are encoded by 12 genes (calS1– calS12)in Arabidopsis thaliana. We evaluated the expression of eight callose synthase genes from Citrus in hybrids between Citrus sunki and Poncirus trifoliata infected with HLB. The objective of this work was to identify possible tolerance loci combining the expression quantitative trait loci (eQTL) of different callose synthases and genetic Single-Nucleotide Polymorphism (SNP) maps of C. sunki and P. trifoliata. The expression data from all CscalS ranged widely among the hybrids. Furthermore, the data allowed the detection of 18 eQTL in the C. sunki map and 34 eQTL in the P. trifoliata map. In both maps, some eQTL for different CscalS were overlapped; thus, a single region could be associated with the regulation of more than one CscalS. The regions identified in this work can be interesting targets for future studies of Citrus breeding programs to manipulate callose synthesis during HLB infection.

摘要 柑橘属植物在全球范围内深受黄龙病（Huanglongbing, HLB）的侵害，造成了显著的经济损失。HLB可引发柑橘生理紊乱，导致胼胝质在韧皮部筛板中沉积。胼胝质由胼胝质合酶催化合成，该酶在拟南芥（Arabidopsis thaliana）中由12个基因（calS1–calS12）编码。本研究针对受HLB侵染的孙基柑橘（Citrus sunki）与枳壳（Poncirus trifoliata）的杂交后代，分析了8个柑橘胼胝质合酶基因的表达水平。本研究的核心目标为：结合不同胼胝质合酶基因的表达数量性状位点（expression quantitative trait loci, eQTL）以及孙基柑橘与枳壳的单核苷酸多态性（Single-Nucleotide Polymorphism, SNP）遗传图谱，筛选潜在的抗病耐受位点。所有CscalS基因的表达数据在杂交后代中呈现出广泛的分布差异。进一步分析显示，在孙基柑橘的遗传图谱中共检测到18个eQTL，在枳壳的遗传图谱中则检测到34个eQTL。在两张遗传图谱中，均存在针对不同CscalS基因的eQTL发生重叠的现象，即单个基因组区域可同时调控多个CscalS基因的表达。本研究鉴定得到的基因组区域，可作为未来柑橘育种项目中调控HLB侵染过程中胼胝质合成的潜在研究靶点。