Centre for Sustainable Food Systems, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Department of Horticulture, University of Wisconsin-Madison, Madison, WI 53706, USA.
G3 (Bethesda). 2021 Dec 8;11(12). doi: 10.1093/g3journal/jkab344.
Geosmin, a degraded sesquiterpene molecule with earthy and musty odor, imbues table beet with its characteristic aroma. Geosmin is heritable and endogenously produced in table beet; its earthy aroma is sought by some consumers but deters others. Geosmin biosynthesis is catalyzed by a bifunctional geosmin synthase enzyme in diverse bacteria and fungi, but a mechanism for geosmin biosynthesis in plants has not been reported. This work employed association analysis and selective genotyping of a segregating F2:3 mapping population to seek QTL associated with geosmin concentration in table beet. GBS reads were aligned to sugar beet reference genome EL10.2, and association analysis revealed two QTL for geosmin concentration on Beta vulgaris ssp. vulgaris chromosome 8. QTL at EL10.2 positions 28,017,624 and 38,488,687 each show effect size 8.7 μg·kg-1 geosmin and explain 8.5% and 6.4% of total variation in geosmin concentration, respectively. Resolution was low due to large recombination bin size and imperfect alignment between the reference genome and mapping population, but population size and selection proportion were sufficient to detect moderate to large effect QTL. This study, the first molecular genetic mapping experiment in table beet, succeeded in finding QTL for geosmin concentration in table beet, and it provides the basis for fine mapping or candidate gene investigation of functional loci for this distinctive sensory trait.
土臭素是一种降解的倍半萜分子，具有泥土和霉味，赋予了食用甜菜特有的香气。土臭素是可遗传的，并且在食用甜菜中内源性产生；它的泥土香气受到一些消费者的追捧，但也令其他消费者望而却步。土臭素生物合成由多种细菌和真菌中的双功能土臭素合酶酶催化，但植物中土臭素生物合成的机制尚未报道。本研究采用分离群体 F2:3 的关联分析和选择性基因分型，寻找与食用甜菜中土臭素浓度相关的 QTL。GBS 读取序列被比对到糖甜菜参考基因组 EL10.2，关联分析揭示了两个与食用甜菜中土臭素浓度相关的 QTL，位于 Beta vulgaris ssp. vulgaris 染色体 8 上的 EL10.2 位置 28,017,624 和 38,488,687，每个 QTL 的效应大小为 8.7μg·kg-1 土臭素，分别解释土臭素浓度总变异的 8.5%和 6.4%。由于重组 bin 大小大且参考基因组与作图群体之间的比对不完美，分辨率较低，但群体大小和选择比例足以检测到中到大效应的 QTL。本研究是食用甜菜中首次分子遗传作图实验，成功找到了食用甜菜中土臭素浓度的 QTL，为该独特感官性状的功能基因座的精细定位或候选基因研究提供了基础。
