Kokane Sunil B, Bhose Sumit, Kokane Amol, Gubyad Mrugendra, Ghosh Dilip Kumar
Plant Virology Laboratory, ICAR-Central Citrus Research Institute, Nagpur, Maharashtra India.
Present Address: Sea6Energy Private Limited, C-CAMP, TIFR-NCBS Campus, Belary Road, Bengaluru, Karnataka 560065 India.
3 Biotech. 2020 Aug;10(8):341. doi: 10.1007/s13205-020-02334-x. Epub 2020 Jul 18.
Huanglongbing (HLB, Citrus greening), caused by a phloem-limited fastidious gram-negative bacterium, " Liberibacter spp.", is one of the devastating diseases of citrus worldwide. The pathogen belongs to the alpha-proteobacteria group and is classified on the basis of its geographical origin and 16S rRNA sequence diversity. Although the disease has been reported from all citrus growing states of India, the status and the molecular variability among the isolates from the Northern part of the country is unknown. A total of five different HLB isolates originating from Northern India showing variable symptoms were studied. The genomic regions of four different genes, i.e., 16S rRNA, intergenic 16S/23S rRNA spacer region, rplA-rplJ, and CLIBASIA_01645 were amplified by PCR, sequenced, and variations in these sequences were assessed. Analysis of 16S rRNA clearly indicated that all five isolates fit in to ' Liberibacter asiaticus' (Las) group. However, 16S/23S rRNA intergenic spacer region-based analysis failed to segregate these isolates beyond species level. Sequence analysis of rplA-rplJ gene and CLIBASIA_01645 loci also confirmed the existence of diversity among the 'Las' in the surveyed areas. Further, 16S rRNA and rplA-rplJ-based SNP analysis revealed that some isolates segregated into three new lineages, two on the basis of 16Sr (16Sr-XV and 16Sr-XVI), and one based on β-rp (rp-IV), respectively. A tandem repeat number (TRN) at CLIBASIA_01645 region were TRN = 5, 6 and 13; with TRN = 6 being common in three 'Las' isolates. Overall, the study demonstrated that all examined five HLB isolates belonged to 'Las' group. However, these isolates showed distinct sequence variability in three out of four genomic regions. The results provide a robust framework for understanding differences in pathogenicity among different HLB isolates as it is plausibly related to their genomic variation, and evolutionary history.
黄龙病（HLB，柑橘绿变病）由一种韧皮部受限的苛求革兰氏阴性细菌“韧皮杆菌属（Liberibacter spp.）”引起，是全球柑橘最具毁灭性的病害之一。该病原体属于α-变形菌纲，根据其地理起源和16S rRNA序列多样性进行分类。尽管印度所有柑橘种植邦都已报道了这种病害，但该国北部地区分离株的状况及其分子变异性尚不清楚。本研究共对来自印度北部的5个表现出不同症状的不同HLB分离株进行了研究。通过PCR扩增了4个不同基因的基因组区域，即16S rRNA、16S/23S rRNA基因间隔区、rplA-rplJ和CLIBASIA_01645，进行了测序，并评估了这些序列中的变异。16S rRNA分析清楚地表明，所有5个分离株均属于‘亚洲韧皮杆菌（Las）’组。然而，基于16S/23S rRNA基因间隔区的分析未能在种水平以上区分这些分离株。rplA-rplJ基因和CLIBASIA_01645位点的序列分析也证实了调查区域内‘Las’之间存在多样性。此外，基于16S rRNA和rplA-rplJ的SNP分析表明，一些分离株分别分为三个新谱系，两个基于16Sr（16Sr-XV和16Sr-XVI），一个基于β-rp（rp-IV）。CLIBASIA_01645区域的串联重复数（TRN）分别为TRN = 5、6和13；TRN = 6在三个‘Las’分离株中常见。总体而言，该研究表明，所有检测的5个HLB分离株均属于‘Las’组。然而，这些分离株在四个基因组区域中的三个区域表现出明显的序列变异性。这些结果为理解不同HLB分离株之间致病性的差异提供了一个有力的框架，因为这可能与其基因组变异和进化历史有关。
