National institute of plant genome rese Delhi, Delhi, India
Body of Abstract: The symbiotic interaction between legumes and rhizobia results in the formation of organs like structures ‘nodules’ following de-differentiation of the legume root cortical cells. Medicago truncatula a model legume forms indeterminate nodules with a persistent apical meristem, followed by invasion, nitrogen-fixing, and senescence zone successively. In the invasion zone of Medicago nodule, rhizobia get endocytosed inside the host cell. Endocytosis leads to the encapsulation of the rhizobia with a plant-derived membrane, that ultimately generates a membrane-bound bacterial unit called ‘symbiosome’. The molecular events and transcriptional regulation during symbiosome development are not well characterized. REGULATOR of SYMBIOSOME DIFFERENTIATION (RSD), a member of Cysteine-2/Histidine-2 family protein, is the only transcription factor that has been reported to have a role during symbiosome development (Sinharoy et al., 2013). Bacteroid differentiation was disrupted in rsd-1 nodules with activation of profound defense response. RSD has been reported as a transcription repressor with an EAR type repressor domain. Overexpression studies, transcriptome analysis, and phylogenetic evidence indicated a dual regulatory role of RSD along with its interacting partners. The latest release of the Medicago genome (v5) deciphered the presence of a long non-coding RNA (lncRNA) overlapping to antisense to RSD-mRNA with a nodule specific expression (Pecrix et al., 2018). Our current understanding of the RSD medicated symbiosome development will be discussed in detail.