Genome-wide exploration and validation of root specific miRNAs contributing towards water conservation in pearl millet

Pearl millet [Pennisetum glaucum (L.) R. Br.] is an important crop of the arid and semi-arid regions of the world. Capable to grow in harsh and marginal environments with the highest degree of tolerance to drought and heat stresses among cereals. Diverse germplasm of pearl millet shows significant phenotypic variation in response to abiotic stresses. This characteristic feature makes pearl millet a unique model among other cereals to study the mechanisms responsible for mitigating divers abiotic stress. Present study, focused on identifying the physiological response of two pearl millet high resolution cross (HRC) genotypes i.e. Vapour pressure deficit (VPD) insensitive genotype (ICMR 1122) and VPD sensitive genotype (ICMR 1152), in response to low and high VPD. ICMR 1152 was found to be to lower transpiration rate (Tr) under high VPD conditions as it showed higher transpiration efficiency and lower root exudation as compared to ICMR 1122. Further, low and high VPD condition and genotype specific Pg-miRs were identified by deep sequencing analysis. A total of 94, 23 known Pg-miRs are 53, 5 novel miRNAs were identified for ICMR 1152 and 1122 genotypes respectively. The Pg-miR165, 168, 170, and 319 family exhibited significant differential expression under low and high VPD conditions in both genotypes. Pg-miRs specific to adventitious roots development and various stress response has been deciphered. Suitable targets for each Pg-miRs were identified and validated expression of top targets in both genotypes responsible for stress. This study shed light upon the role of miRNAs in regulation of drought tolerance in pearl millet.

珍珠粟（Pearl millet）[狼尾草属（Pennisetum glaucum (L.) R. Br.）]是全球干旱与半干旱区域的重要作物。该谷类作物可在严苛边际环境中生长，且在所有谷类作物中对干旱、热胁迫的耐受性最强。珍珠粟的多样化种质资源在应对非生物胁迫时呈现出显著的表型变异，这一特性使其成为研究谷类作物缓解多样非生物胁迫机制的独特模型。本研究聚焦于解析两个珍珠粟高分辨率杂交（high resolution cross, HRC）基因型对高低水汽压亏缺（Vapour pressure deficit, VPD）的生理响应，即水汽压亏缺不敏感基因型ICMR 1122与水汽压亏缺敏感基因型ICMR 1152。研究发现，相较于ICMR 1122，ICMR 1152在高水汽压亏缺条件下蒸腾速率（transpiration rate, Tr）更低，这与其更高的蒸腾效率及更低的根系分泌物（root exudation）水平相关。进一步通过深度测序（deep sequencing）分析，本研究鉴定得到了高低水汽压亏缺条件下以及基因型特异性的Pg-miRNA。其中，ICMR 1152与ICMR 1122基因型分别鉴定到94个已知Pg-miRNA与53个新miRNA，以及23个已知Pg-miRNA与5个新miRNA。Pg-miR165、168、170及319家族在两个基因型的高低水汽压亏缺条件下均呈现显著差异表达。本研究还解析了与不定根发育及多种胁迫响应相关的特异性Pg-miRNA。研究人员为每个Pg-miRNA鉴定得到了适宜的靶基因，并验证了两个基因型中参与胁迫响应的核心靶基因的表达情况。本研究揭示了miRNA在调控珍珠粟耐旱性中的关键作用。