The Nod factor-independent nodulation in Aeschynomene evenia required the common plant-microbe symbiotic "toolkit"

Abstract

Nitrogen fixation in the legume-rhizobium symbiosis is a crucial area of research for more sustainable agriculture. Our knowledge of the plant cascade in response to the perception of bacterial Nod factors has increased in recent years. However, the discovery that Nod factors are not involved in the Aeschynomene-Bradyrhizobium spp. interaction suggests that alternative molecular dialogues may exist in the legume family. We evaluated the conservation of the signaling pathway common to other endosymbioses using three candidate genes: Ca 2+

Transcriptomic analysis with the progress of symbiosis in ‘crack-entry’ legumeArachis hypogaeahighlights its contrast with ‘infection thread’ adapted legumes

“…The infection pockets observed at 4dpi act as infection zone (IZ) founder cells and it is their uniform division and differentiation that give rise to the distinct aeschynomenoid type IZ in mature nodules. There has not been a single case where uninfected primordium was noted, which is in accordance with the proposition of infection preceding development of aeschynomenoid nodules (Fabre et al, 2015). By 8dpi there was visible nodule-like structure at the lateral-root base ( Fig.…”

“…Though cytokinin signaling is important for nodule development in both 'crack-entry' and IT adapted legumes (Gonzalez-Rizzo et al, 2006;Fabre et al, 2015;Kundu and DasGupta, 2017), PCA revealed distinct expression pattern for several downstream factors in A. hypogaea as compared to model legumes. For example, homologue of MtRR1, a type-B RR has a distinct expression pattern in A hypogaea and unlike model legumes, its downstream transcription factor…”

“…(Sprent and James, 2007). In these legumes, rhizobia directly access the cortical cells for development of their nodule primordia and the infected cells repeatedly divide to develop the mature nodule with aeschynomenoid infection zone (IZ) devoid of uninfected cells (Boogerd and Rossum, 1997;Fabre et al, 2015). Very limited information is available for 'crack-entry' legumes from dalbergioid/genistoid clade which are basal in their divergence within the papilionoideae.…”

A phylogenetic framework of the legume genusAeschynomenefor comparative genetic analysis of the Nod-dependent and Nod-independent symbioses

“…EPR3 and RPG ), and nodule functioning (e.g. DNF2 and FEN1 ) were found not to be expressed in A. evenia roots and nodules, based on RNAseq data (Czernic et al ., 2015; Fabre et al ., 2015; Chaintreuil et al ., 2016a; Nouwen et al ., 2017). This suggested that the Nod-independent symbiosis is distinct from the Nod-dependent one.…”

Molecular Basis of Root Nodule Symbiosis between Bradyrhizobium and ‘Crack-Entry’ Legume Groundnut (Arachis hypogaea L.)

“…[12]. In these crop species, rhizobia directly access the cortical cells to develop nodule primordia, and the infected cells divide repeatedly to form a mature aeschynomenoid nodule in which the core of the infected zone remains separated from uninfected cells [13].…”