Role of transcription factor NIN - Molecular Biology

The role of the key transcription factor NIN during Medicago nodule development

Legume-Rhizobium symbiosis results in the formation of root nodules where bacteria are accommodated intracellularly, differentiate and become able to fix atmospheric nitrogen into ammonia. Medicago (Medicago truncatula ) nodule organogenesis involves the local mitotic activation of root cells by which nodule primordia are formed. Rhizobia (Sinorhizobium meliloti) invade roots through tube-like structures called infection threads. Their formation is initiated in root hairs and they grow towards the nodule primordia. There rhizobia are released into cortical derived cells and these cells become the basal part of the nodule and they host thousands of nitrogen fixing bacteria. Meanwhile, an apical meristem develops and provides new cells to the growing nodule.


The transcription factor NODULE INCEPTION (NIN), that is specifically expressed during nodulation, plays a key role in infection thread formation and nodule organogenesis and coordinates these two processes. Further, NIN is also involved in later stages of nodule development, namely in bacterial release and differentiation.


The aim of the BSc/MSc project is to unravel the role of NIN during nodule development by using various nin mutants (one of them is shown in Fig. 1) and different techniques including molecular cloning, Agrobacterium rhizogenes-mediated root transformation, light and confocal microscopy, RNA in situ hybridization, qPCR and RNAseq.

Figure 1. The nin mutant is defective in bacterial differentiation in nodules. (A) WT nodule is pink because it contains leghemoglobin. (B) In contrast, nin mutant forms white nodules. (C) Differentiated elongated bacteria (green) in WT nodules (C) and (D) non-differentiated small bacteria in mutant nodule. C, D are confocal images. Rhizobia expressing GFP were used for inoculation of roots.
Figure 1. The nin mutant is defective in bacterial differentiation in nodules. (A) WT nodule is pink because it contains leghemoglobin. (B) In contrast, nin mutant forms white nodules. (C) Differentiated elongated bacteria (green) in WT nodules (C) and (D) non-differentiated small bacteria in mutant nodule. C, D are confocal images. Rhizobia expressing GFP were used for inoculation of roots.