Terminal Bacteroid Differentiation Is Associated With Variable Morphological Changes in Legume Species Belonging to the Inverted Repeat-Lacking Clade

Abstract

Medicago and closely related legume species from the inverted repeat-lacking clade (IRLC) impose terminal differentiation onto their bacterial endosymbionts, manifested in genome endoreduplication, cell enlargement, and loss of cell-division capacity. Nodule-specific cysteine-rich (NCR) secreted host peptides are plant effectors of this process. As bacteroids in other IRLC legumes, such as Cicer arietinum and Glycyrrhiza lepidota, were reported not to display features of terminal differentiation, we investigated the fate of bacteroids in species from these genera as well as in four other species representing distinct genera of the phylogenetic tree for this clade. Bacteroids in all tested legumes proved to be larger in size and DNA content than cultured cells; however, the degree of cell elongation was rather variable in the different species. In addition, the reproductive ability of the bacteroids isolated from these legumes was remarkably reduced. In all IRLC species with available sequence data, the existence of NCR genes was found. These results indicate that IRLC legumes provoke terminal differentiation of their endosymbionts with different morphotypes, probably with the help of NCR peptides.

Interdependency of efficient nodulation and arbuscular mycorrhization inPiptadenia gonoacantha,a Brazilian legume tree

“…Spherical bacteroids (“Type S”) were first described in Arachis (Staphorst & Strijdom, ) and Aeschynomene (Bonaldi et al, ), within Papilionoideae. More recently, they were described in Cicer and Ononis (Montiel et al, ), both still within this subfamily. Our study has provided evidence that the bacteroid S‐shape may be naturally distributed within the whole taxonomic range of the nodulated legumes, including members of the Mimosoid clade within the Caesalpinioideae (LPWG, ).…”

Terminal bacteroid differentiation in the legume−rhizobium symbiosis: nodule‐specific cysteine‐rich peptides and beyond

“…It is not known at the moment whether liquorice produces NCR peptides. Nevertheless, this plant triggers TBD of rhizobia upon nodulation by Mesorhizobium tianshanense (Montiel et al ., ). This strain‐specific phenotype (Fig.…”

The evolution of determinate and indeterminate nodules within the Papilionoideae subfamily

“…Glycyrrhiza uralensis, Oxytropis lamberti, Astragalus canadensis, Onobrychis viciifolia, Galega orientalis, Ononis spinosa, Cicer arietinum, Pisum sativum, and Medicago sativa) also have NCR families, but in general they are smaller than the Medicago NCR family. For example, 353 NCR transcripts were identified in pea and C. arietinum has 63 putative NCR genes (Alves-Carvalhoet al, 2015;Montiel et al, 2016;Montiel et al, 2017). NCRs in all the studied IRLC clade species share conserved cysteine spacing pattern, containing 4 or 6 cysteines (Fig.…”