National Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Life Sciences, Nanjing Agricultural University, Nanjing, China.
BMC Genomics. 2018 Sep 26;19(1):709. doi: 10.1186/s12864-018-5109-8.
Metal tolerance is often an integrative result of metal uptake and distribution, which are fine-tuned by a network of signaling cascades and metal transporters. Thus, with the goal of advancing the molecular understanding of such metal homeostatic mechanisms, comparative RNAseq-based transcriptome analysis was conducted to dissect differentially expressed genes (DEGs) in maize roots exposed to cadmium (Cd) stress.
To unveil conserved Cd-responsive genes in cereal plants, the obtained 5166 maize DEGs were compared with 2567 Cd-regulated orthologs in rice roots, and this comparison generated 880 universal Cd-responsive orthologs groups composed of 1074 maize DEGs and 981 rice counterparts. More importantly, most of the orthologous DEGs showed coordinated expression pattern between Cd-treated maize and rice, and these include one large orthologs group of pleiotropic drug resistance (PDR)-type ABC transporters, two clusters of amino acid transporters, and 3 blocks of multidrug and toxic compound extrusion (MATE) efflux family transporters, and 3 clusters of heavy metal-associated domain (HMAD) isoprenylated plant proteins (HIPPs), as well as all 4 groups of zinc/iron regulated transporter protein (ZIPs). Additionally, several blocks of tandem maize paralogs, such as germin-like proteins (GLPs), phenylalanine ammonia-lyases (PALs) and several enzymes involved in JA biosynthesis, displayed consistent co-expression pattern under Cd stress. Out of the 1074 maize DEGs, approximately 30 maize Cd-responsive genes such as ZmHIPP27, stress-responsive NAC transcription factor (ZmSNAC1) and 9-cis-epoxycarotenoid dioxygenase (NCED, vp14) were also common stress-responsive genes reported to be uniformly regulated by multiple abiotic stresses. Moreover, the aforementioned three promising Cd-upregulated genes with rice counterparts were identified to be novel Cd-responsive genes in maize. Meanwhile, one maize glutamate decarboxylase (ZmGAD1) with Cd co-modulated rice ortholog was selected for further analysis of Cd tolerance via heterologous expression, and the results suggest that ZmGAD1 can confer Cd tolerance in yeast and tobacco leaves.
These novel findings revealed the conserved function of Cd-responsive orthologs and paralogs, which would be valuable for elucidating the genetic basis of the plant response to Cd stress and unraveling Cd tolerance genes.
金属耐受性通常是金属摄取和分布的综合结果，而金属摄取和分布则由信号级联和金属转运蛋白网络精细调节。因此，为了深入了解这种金属稳态机制的分子机制，我们进行了基于比较 RNAseq 的转录组分析，以剖析暴露于镉（Cd）胁迫下的玉米根中的差异表达基因（DEGs）。
为了揭示谷类植物中保守的 Cd 响应基因，将获得的 5166 个玉米 DEGs 与水稻根中 2567 个 Cd 调控的同源基因进行比较，比较产生了由 1074 个玉米 DEGs 和 981 个水稻同源基因组成的 880 个通用 Cd 响应同源基因簇。更重要的是，大多数同源 DEGs 显示出 Cd 处理的玉米和水稻之间协调的表达模式，其中包括一大类多药耐药（PDR）型 ABC 转运蛋白、两个氨基酸转运蛋白簇、3 个多药和毒性化合物外排（MATE）外排家族转运蛋白块以及 3 个重金属相关结构域（HMAD）异戊二烯化植物蛋白（HIPP）簇，以及锌/铁调节转运蛋白（ZIP）的 4 个簇。此外，一些玉米串联同源基因簇，如几丁质酶类似蛋白（GLPs）、苯丙氨酸解氨酶（PALs）和参与 JA 生物合成的几种酶，在 Cd 胁迫下表现出一致的共表达模式。在 1074 个玉米 DEGs 中，大约 30 个玉米 Cd 响应基因，如 ZmHIPP27、应激响应 NAC 转录因子（ZmSNAC1）和 9-顺式-环氧类胡萝卜素双加氧酶（NCED，vp14），也被报道为受多种非生物胁迫均匀调节的通用应激响应基因。此外，还鉴定出与水稻同源基因相对应的上述三个有希望的 Cd 上调基因，它们是玉米中新型 Cd 响应基因。同时，选择一个具有 Cd 共调节水稻同源物的玉米谷氨酸脱羧酶（ZmGAD1）进行异源表达，以进一步分析 Cd 耐受性，结果表明 ZmGAD1 可以在酵母和烟草叶片中赋予 Cd 耐受性。
这些新发现揭示了 Cd 响应同源物和同系物的保守功能，这对于阐明植物对 Cd 胁迫的反应的遗传基础和揭示 Cd 耐受基因将是有价值的。
