Fonseca-García Citlali, Zayas Alejandra E, Montiel Jesús, Nava Noreide, Sánchez Federico, Quinto Carmen
Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad 2001, Colonia Chamilpa, Cuernavaca, Morelos, 62210, Mexico.
Department of Molecular Biology and Genetics, Aarhus University, C 8000, Aarhus, Denmark.
BMC Genomics. 2019 Nov 4;20(1):800. doi: 10.1186/s12864-019-6162-7.
Reactive oxygen species (ROS) are generated by NADPH oxidases known as respiratory burst oxidase homologs (RBOHs) in plants. ROS regulate various cellular processes, including the mutualistic interactions between legumes and nitrogen-fixing bacteria or arbuscular mycorrhizal (AM) fungi. Rboh is a multigene family comprising nine members (RbohA-I) in common bean (Phaseolus vulgaris). The RNA interference-mediated silencing of RbohB (PvRbohB-RNAi) in this species diminished its ROS production and greatly impaired nodulation. By contrast, the PvRbohB-RNAi transgenic roots showed early hyphal root colonization with enlarged fungal hypopodia; therefore, we proposed that PvRbohB positively regulates rhizobial infection (Rhizobium tropici) and inhibits AM colonization by Rhizophagus irregularis in P. vulgaris.
To corroborate this hypothesis, an RNA-Seq transcriptomic analysis was performed to identify the differentially expressed genes in the PvRbohB-RNAi roots inoculated with Rhizobium tropici or Rhizophagus irregularis. We found that, in the early stages, root nodule symbioses generated larger changes of the transcriptome than did AM symbioses in P. vulgaris. Genes related to ROS homeostasis and cell wall flexibility were markedly upregulated in the early stages of rhizobial colonization, but not during AM colonization. Compared with AM colonization, the rhizobia induced the expression of a greater number of genes encoding enzymes involved in the metabolism of auxins, cytokinins, and ethylene, which were typically repressed in the PvRbohB-RNAi roots.
Our research provides substantial insights into the genetic interaction networks in the early stages of rhizobia and AM symbioses with P. vulgaris, as well as the differential roles that RbohB plays in processes related to ROS scavenging, cell wall remodeling, and phytohormone homeostasis during nodulation and mycorrhization in this legume.
活性氧（ROS）由植物中称为呼吸爆发氧化酶同源物（RBOHs）的NADPH氧化酶产生。ROS调节各种细胞过程，包括豆科植物与固氮细菌或丛枝菌根（AM）真菌之间的共生相互作用。Rboh是一个多基因家族，在普通菜豆（Phaseolus vulgaris）中由九个成员（RbohA - I）组成。该物种中RNA干扰介导的RbohB（PvRbohB - RNAi）沉默减少了其ROS产生，并极大地损害了结瘤。相比之下，PvRbohB - RNAi转基因根表现出早期菌丝根定殖，真菌附着胞增大；因此，我们提出PvRbohB正向调节热带根瘤菌的感染，并抑制不规则球囊霉在普通菜豆中的AM定殖。
为了证实这一假设，进行了RNA测序转录组分析，以鉴定接种热带根瘤菌或不规则球囊霉的PvRbohB - RNAi根中差异表达的基因。我们发现，在早期阶段，普通菜豆中根瘤共生比AM共生引起的转录组变化更大。与ROS稳态和细胞壁柔韧性相关基因在根瘤菌定殖早期显著上调，但在AM定殖期间没有上调。与AM定殖相比，根瘤菌诱导了更多编码参与生长素、细胞分裂素和乙烯代谢的酶的基因表达，这些基因在PvRbohB - RNAi根中通常受到抑制。
我们的研究为普通菜豆根瘤菌和AM共生早期阶段的遗传相互作用网络，以及RbohB在该豆科植物结瘤和菌根形成过程中与ROS清除、细胞壁重塑和植物激素稳态相关过程中发挥差异作用提供了重要见解。
