The TIR (Toll/interleukin-1 receptor) domain has been proposed to play a signalling role in resistance responses mediated by TIR-containing proteins. The functions of some TIR-domain-containing proteins have been defined in some plants; however, there has been no study evaluating TIR-domain-containing proteins in soybean (Glycine max (L.) Merr.). In this study, GmTIR was isolated from soybean, and its functions under stresses were analysed. Analysis of tissue-specific expression patterns showed that GmTIR was strongly expressed in leaves and weakly expressed in the immature green beans. Treatments with Phytophthora sojae, salicylic acid, methyl jasmonate, abscisic acid, copper, salt and drought significantly increased GmTIR expression, and 1-aminocyclopropane-1-carboxylic acid and low temperature caused slight increases. Compared with wild type expression, GmTIR overexpression in Arabidopsis thaliana led to a higher germination rate under both salt and drought stresses, but the root length of transgenic Arabidopsis was greater than of wild type plants only under salt stress. In response to the stresses, accumulation of proline in transgenic plants was also higher. The results suggest that GmTIR could be a positive factor for promoting the survival of plants under biotic and abiotic stresses.

Pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) is initiated upon PAMP recognition by pattern recognition receptors (PRR). PTI signals are transmitted through activation of mitogen-activated protein kinases (MAPKs), inducing signaling and defense processes such as reactive oxygen species (ROS) production and callose deposition. Here, we examine mutants for two Arabidopsis thaliana genes encoding homologs of UBIQUITIN-ASSOCIATED DOMAIN-CONTAINING PROTEIN 2 (UBAC2), a conserved endoplasmic reticulum (ER) protein implicated in ER protein quality control. The ubac2 mutants were hypersusceptible to a type III secretion-deficient strain of the bacterial pathogen Pseudomonas syringae, indicating a PTI defect. The ubac2 mutants showed normal PRR biogenesis, MAPK activation, ROS burst, and PTI-associated gene expression. Pathogen- and PAMP-induced callose deposition, however, was compromised in ubac2 mutants. UBAC2 proteins interact with the plant-specific long coiled-coil protein PAMP-INDUCED COILED COIL (PICC), and picc mutants were compromised in callose deposition and PTI. Compromised callose deposition in the ubac2 and picc mutants was associated with reduced accumulation of the POWDERY MILDEW RESISTANT 4 (PMR4) callose synthase, which is responsible for pathogen-induced callose synthesis. Constitutive overexpression of PMR4 restored pathogen-induced callose synthesis and PTI in the ubac2 and picc mutants. These results uncover an ER pathway involving the conserved UBAC2 and plant-specific PICC proteins that specifically regulate pathogen-induced callose deposition in plant innate immunity.

Table S2. qRT-PCR primers. (XLSX 9 kb)

BACKGROUND:The 100-pod fresh weight (PFW), 100-seed fresh weight (SFW), 100-seed dry weight (SDW) and moisture content of fresh seeds (MCFS) at the R6 stage are crucial factors for vegetable soybean yield. However, the genetic basis of yield at the R6 stage remains largely ambiguous in soybean.RESULTS:To better understand the molecular mechanism underlying yield, we investigated four yield-related traits of 133 soybean landraces in two consecutive years and conducted a genome-wide association study (GWAS) using 82,187 single nucleotide polymorphisms (SNPs). The GWAS results revealed a total of 14, 15, 63 and 48 SNPs for PFW, SFW, SDW and MCFS, respectively. Among these markers, 35 SNPs were repeatedly identified in all evaluated environments (2015, 2016, and the average across the two years), and most co-localized with yield-related QTLs identified in previous studies. AX-90496773 and AX-90460290 were large-effect markers for PFW and MCFS, respectively. The two markers were stably identified in all environments and tagged to linkage disequilibrium (LD) blocks. Six potential candidate genes were predicted in LD blocks; five of them showed significantly different expression levels between the extreme materials with large PFW or MCFS variation at the seed development stage. Therefore, the five genes Glyma.16g018200, Glyma.16g018300, Glyma.05g243400, Glyma.05g244100 and Glyma.05g245300 were regarded as candidate genes associated with PFW and MCFS.CONCLUSION:These results provide useful information for the development of functional markers and exploration of candidate genes in vegetable soybean high-yield breeding programs.

The mediator complex is an essential link between transcription factors and RNA polymerase II, and mainly functions in the transduction of diverse signals to genes involved in different pathways. Limited information is available on the role of soybean mediator subunits in growth and development, and their participation in defense response regulation. Here, we performed genome-wide identification of the 95 soybean mediator subunits, which were unevenly localized on the 20 chromosomes and only segmental duplication events were detected. We focused on GmMED16-1, which is highly expressed in the roots, for further functional analysis. Transcription of GmMED16-1 was induced in response to Phytophthora sojae infection. Agrobacterium rhizogenes mediated soybean hairy root transformation was performed for the silencing of the GmMED16-1 gene. Silencing of GmMED16-1 led to an enhanced susceptibility phenotype and increased accumulation of P. sojae biomass in hairy roots of transformants. The transcript levels of NPR1, PR1a, and PR5 in the salicylic acid defense pathway in roots of GmMED16-1-silenced transformants were lower than those of empty-vector transformants. The results provide evidence that GmMED16-1 may participate in the soybean–P. sojae interaction via a salicylic acid-dependent process.

Selective macroautophagy/autophagy targets specific cargo by autophagy receptors through interaction with ATG8 (autophagy-related protein 8)/MAP1LC3 (microtubule associated protein 1 light chain 3) for degradation in the vacuole. Here, we report the identification and characterization of 3 related ATG8-interacting proteins (AT1G17780/ATI3A, AT2G16575/ATI3B and AT1G73130/ATI3C) from Arabidopsis. ATI3 proteins contain a WxxL LC3-interacting region (LIR) motif at the C terminus required for interaction with ATG8. ATI3 homologs are found only in dicots but not in other organisms including monocots. Disruption of ATI3A does not alter plant growth or development but compromises both plant heat tolerance and resistance to the necrotrophic fungal pathogen Botrytis cinerea. The critical role of ATI3A in plant stress tolerance and disease resistance is dependent on its interaction with ATG8. Disruption of ATI3B and ATI3C also significantly compromises plant heat tolerance. ATI3A interacts with AT3G56740/UBAC2A and AT2G41160/UBAC2B (Ubiquitin-associated [UBA] protein 2a/b), 2 conserved proteins implicated in endoplasmic reticulum (ER)-associated degradation. Disruption of UBAC2A and UBAC2B also compromised heat tolerance and resistance to B. cinerea. Overexpression of UBAC2 induces formation of ATG8- and ATI3-labeled punctate structures under normal conditions, likely reflecting increased formation of phagophores or autophagosomes. The ati3 and ubac2 mutants are significantly compromised in sensitivity to tunicamycin, an ER stress-inducing agent, but are fully competent in autophagy-dependent ER degradation under conditions of ER stress when using an ER lumenal marker for detection. We propose that ATI3 and UBAC2 play an important role in plant stress responses by mediating selective autophagy of specific unknown ER components.