Proliferation of legume nodule primordia is controlled by shoot-root signaling known as autoregulation of nodulation (AON). Mutants defective in AON show supernodulation and increased numbers of lateral roots. Here, we demonstrate that AON in soybean is controlled by the receptor-like protein kinase GmNARK (Glycine max nodule autoregulation receptor kinase), similar to Arabidopsis CLAVATA1 (CLV1). Whereas CLV1 functions in a protein complex controlling stem cell proliferation by short-distance signaling in shoot apices, GmNARK expression in the leaf has a major role in long-distance communication with nodule and lateral root primordia.
BackgroundWe present the genome sequence of the tammar wallaby, Macropus eugenii, which is a member of the kangaroo family and the first representative of the iconic hopping mammals that symbolize Australia to be sequenced. The tammar has many unusual biological characteristics, including the longest period of embryonic diapause of any mammal, extremely synchronized seasonal breeding and prolonged and sophisticated lactation within a well-defined pouch. Like other marsupials, it gives birth to highly altricial young, and has a small number of very large chromosomes, making it a valuable model for genomics, reproduction and development.ResultsThe genome has been sequenced to 2 × coverage using Sanger sequencing, enhanced with additional next generation sequencing and the integration of extensive physical and linkage maps to build the genome assembly. We also sequenced the tammar transcriptome across many tissues and developmental time points. Our analyses of these data shed light on mammalian reproduction, development and genome evolution: there is innovation in reproductive and lactational genes, rapid evolution of germ cell genes, and incomplete, locus-specific X inactivation. We also observe novel retrotransposons and a highly rearranged major histocompatibility complex, with many class I genes located outside the complex. Novel microRNAs in the tammar HOX clusters uncover new potential mammalian HOX regulatory elements.ConclusionsAnalyses of these resources enhance our understanding of marsupial gene evolution, identify marsupial-specific conserved non-coding elements and critical genes across a range of biological systems, including reproduction, development and immunity, and provide new insight into marsupial and mammalian biology and genome evolution.
SUMMARYTwo allelic non-nodulating mutants, nod49 and rj1, were characterized using map-based cloning and candidate gene approaches, and genetic complementation. From our results we propose two highly related lipo-oligochitin LysM-type receptor kinase genes (GmNFR1a and GmNFR1b) as putative Nod factor receptor components in soybean. Both mutants contained frameshift mutations in GmNFR1a that would yield protein truncations. Both mutants contained a seemingly functional GmNFR1b homeologue, characterized by a 374-bp deletion in intron 6 and 20-100 times lower transcript levels than GmNFR1a, yet both mutants were unable to form nodules. Mutations in GmNFR1b within other genotypes had no defects in nodulation, showing that GmNFR1b was redundant. Transgenic overexpression of GmNFR1a, but not of GmNFR1b, increased nodule number per plant, plant nitrogen content and the ability to form nodules with restrictive, ultra-low Bradyrhizobium japonicum titres in transgenic roots of both nod49 and rj1. GmNFR1a overexpressing roots also formed nodules in nodulation-restrictive acid soil (pH 4.7). Our results show that: (i) NFR1a expression controls nodule number in soybean, and (ii) acid soil tolerance for nodulation and suppression of nodulation deficiency at low titre can be achieved by overexpression of GmNFR1a.
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