Nitrogen‐fixing rhizobia and legumes have developed complex mutualistic mechanism that allows to convert atmospheric nitrogen into ammonia. Signalling by mitogen‐activated protein kinases (MAPKs) seems to be involved in this symbiotic interaction. Previously, we reported that stress‐induced MAPK (SIMK) shows predominantly nuclear localization in alfalfa root epidermal cells. Nevertheless, SIMK is activated and relocalized to the tips of growing root hairs during their development. SIMK kinase (SIMKK) is a well‐known upstream activator of SIMK. Here, we characterized production parameters of transgenic alfalfa plants with genetically manipulated SIMK after infection with Sinorhizobium meliloti. SIMKK RNAi lines, causing strong downregulation of both SIMKK and SIMK, showed reduced root hair growth and lower capacity to form infection threads and nodules. In contrast, constitutive overexpression of GFP‐tagged SIMK promoted root hair growth as well as infection thread and nodule clustering. Moreover, SIMKK and SIMK downregulation led to decrease, while overexpression of GFP‐tagged SIMK led to increase of biomass in above‐ground part of plants. These data suggest that genetic manipulations causing downregulation or overexpression of SIMK affect root hair, nodule and shoot formation patterns in alfalfa, and point to the new biotechnological potential of this MAPK.

中文翻译：

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苜蓿 SIMK 的过度表达促进根毛生长、根瘤聚集和地上部生物量生产

固氮根瘤菌和豆科植物已经发展出复杂的互利机制，可以将大气中的氮转化为氨。丝裂原激活蛋白激酶（MAPK）的信号传导似乎参与了这种共生相互作用。此前，我们报道了应激诱导的 MAPK (SIMK) 在苜蓿根表皮细胞中主要表现为核定位。然而，SIMK 在根毛发育过程中被激活并重新定位到生长的根毛尖端。SIMK 激酶 (SIMKK) 是众所周知的 SIMK 上游激活剂。在这里，我们用基因操作的 SIMK 表征了苜蓿中华根瘤菌感染后转基因苜蓿植物的生产参数。SIMKK RNAi系引起SIMKK和SIMK的强烈下调，显示出根毛生长减少以及形成感染线和结节的能力较低。相反，GFP标记的SIMK的组成型过度表达促进根毛生长以及感染线和根瘤聚集。此外，SIMKK和SIMK的下调导致植物地上部分生物量的减少，而GFP标记的SIMK的过度表达导致植物地上部分生物量的增加。这些数据表明，导致 SIMK 下调或过度表达的基因操作会影响苜蓿的根毛、根瘤和芽形成模式，并指出该 MAPK 的新生物技术潜力。