Parallel domestication with broad mutational spectrum of determinate stem growth habit in leguminous crops.[Pubmed: 30112860]

Stem growth habit is a key plant architecture trait determining yield potential in grain legumes, and phenotypic changes from indeterminate stem growth habit of wild mungbeans (Vigna radiata) to determinate stem growth habit of cultivated mungbeans is a critical domestication transition. Here we show that indeterminate stem in wild mungbean is modulated by a single gene VrDet1, which encodes a signaling protein of shoot apical meristems. The transition from indeterminate to determinate stem growth habit was achieved by selection of two linked point mutations in two putative cis-regulatory elements, resulting in significant reduction in gene expression. Both the wild-type nucleotides corresponding to the two point mutations were essential for the VrDet1 function. In addition, two highly diverse haplotypes of Vrdet1 were found in cultivated mungbeans, suggesting duel domestication of Vrdet1. VrDet1 was orthologous to Dt1 in wild soybean and PvTFL1y in wild common bean, where multiple loss-of-function mutations altering individual genes' coding sequences were selected to produce determinate stems in cultivated accessions. Interspecific comparison of these orthologs in the wild and cultivated accessions reveals the most conservative interspecific and intraspecific parallel domestication events with the broadest mutational spectrum of a domestication trait in leguminous crops. We also found that interspecifically and functionally conserved promoters possess cis-regulatory elements that are highly conserved in kind but greatly variable in number and order, demonstrating the evolutionary dynamics of regulatory sequences. This work provides insights into the origins of cultivated mungbean and exemplifies the conservativeness and plasticity of the domestication processes of related crops. This article is protected by copyright. All rights reserved.

Loss of NifQ leads to accumulation of porphyrins and altered metal-homeostasis in nitrogen-fixing symbioses.[Pubmed: 30070615]

Symbiotic nitrogen fixation between legumes and rhizobia involves a coordinated expression of many plant and bacterial genes as well as finely tuned metabolic activities of micro- and macro-symbionts. In spite of such complex interactions, symbiotic proficiency remains a resilient process with host plants apparently capable of compensating for some deficiencies in rhizobia. What controls nodule homeostasis is still poorly understood and probably varies between plant species. In this respect, the promiscuous Sinorhizobium (Ensifer) fredii strain NGR234 has become a model to assess the relative contribution of single gene products to many symbioses. Here, we describe how a deletion in nifQ of NGR234 (strain NGRΔnifQ) makes nodules of Vigna unguiculata, Vigna radiata and Macroptilium atropurpureum but not of the mimisoid tree Leucaena leucocephala, purple red. This peculiar dark-nodule phenotype did not necessarily correlate with a decreased proficiency of NGRΔnifQ, but coincided with a twenty-fold or more accumulation of coproporphyrin III and uroporphyrin III in V. unguiculata nodules. Porphyrin accumulation was not restricted to plant cells infected with bacteroids but also extended to nodule cortex. Nodule metal-homeostasis was altered but not sufficiently to prevent assembly and functioning of nitrogenase. Although NifQ role in donating molybdenum during assembly of nitrogenase cofactor FeMo-co makes it essential in free-living diazotrophs, our results highlight NifQ dispensability in many legume species.