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Tillering is one of the most important determinants of biomass and yield in rice (Oryza sativa L.). The capacity of plants to develop tillers from primordial meristems or buds is determined not only by the genotype but also by environmental cues. Here, we characterized the function of rice grassy tiller1 (OsGT1) and its interaction with other genetic and biological factors involved in tiller bud outgrowth in rice by generating OsGT1 RNA interference (RNAi) and overexpression (OX) lines. The tiller number was increased in OsGT1-RNAi mutants but strongly suppressed in OsGT1-OX lines. Expression analysis of OsGT1 in rice phyB mutants and in genotypes carrying various genetic combinations of GT1 RNAi and phyB demonstrated that OsGT1 is not involved in phyB-mediated suppression of tiller development in rice. Expression analysis of fine culm1 (fc1), a rice tb1 homolog, and molecular assays demonstrated that FC1 enhances the expression of OsGT1 by directly binding to its promoter. Comparison of the transcriptomic profiles of fc1 and OsGT1-RNAi mutants revealed differentially expressed genes (DEGs) common to both genotypes. Finally, analysis of tillering phenotypes of OX and RNAi seedlings treated with various phytohormones implied a possible role of OsGT1 in strigolactone-mediated tiller outgrowth. Overall, this study enhances our understanding of the diverse mechanisms of tiller development in grasses.

The AMT1 family comprises major ammonium transporters in rice roots. In this study, we utilized AMT1 RNAi mutants (amt1) to explore how AMT1 affects NH4+- and NO3–-mediated morphological development and NH4+-responsive gene expression in roots. In the presence of NH4+, amt1 showed inhibition of NO3–- dependent lateral root development. The inhibitory action of NH4+ on lateral root growth was independent of the NO3– concentrations supplied to amt1 roots. The results of split root assays indicated that NH4+ exerts systemic action in inhibiting NO3–-dependent lateral root development in amt1. Further study with NAA and NOA, a potent auxin flux inhibitor, suggested that perturbation of membrane dynamics might not be the primary cause of the inhibitory action of NH4+ on NO3–-mediated lateral root growth in amt1 mutants. RNA-seq analysis of NH4+-responsive genes showed that approximately half of DEGs observed in wild-type roots were not detected in the DEGs of amt1 roots. Gene ontology enrichment analysis suggested that the expression of specific functional gene groups were affected by amt1 during the early response to NH4+. Auxin-responsive gene expression and root gravity responses were altered in amt1. This study demonstrated that AMT1 affects the interactions not only between ammonium and nitrate in lateral root growth but also between auxin and NH4+ in rice roots.

Sheath blight disease (ShB) severely affects rice production; however, the details of defense against ShB remain unclear. To understand the rice defense mechanism against ShB, an RNA sequencing analysis was performed using Rhizoctonia solani inoculated rice leaves after 48 h of inoculation. Among them, 3417 genes were upregulated and 2532 were downregulated when compared with the control group (> twofold or

NH4+ is an important nitrogen resource for rice plants in paddy soil. Therefore, it is likely that NH4+-triggered plant growth interacts with phytohormone-mediated developmental mechanisms. Our previous transcriptomic analysis revealed that many genes involved in auxin signaling and efflux are sensitive to NH4+. In the current study, we found that NH4+ treatment causes a delayed gravity response in rice roots. To further elucidate the interlocking relationship between NH4+ and auxin signaling during root development, we utilized mutants and overexpressors of a key NH4+ signaling transcription factor INDETERMINATE DOMAIN 10 (IDD10), encoding a transcription factor that regulates the expression of NH4+ uptake and N-assimilation genes. We obtained several lines of evidence that auxin affects NH4+-mediated gene expression and root development in rice plants via IDD10. First, the gravity response was delayed in idd10 roots and accelerated in IDD10 overexpressor (IDD10 OX) roots in the absence and (especially) presence of NH4+. Second, idd10 plants showed strong root coiling only in the presence of NH4+. However, treatment of 1-N-naphthylphthalamic acid (NPA), a polar auxin transport inhibitor suppressed the NH4+-specific root phenotype of idd10. Third, the expression of NH4+-responsive auxin-related genes was affected in idd10 and IDD10 overexpressors. Finally, IDD10 expression was induced by IAA and suppressed by NPA. These findings suggest that the gene expression patterns and phenotypes triggered by NH4+ are influenced by the actions of auxin during root development, pointing to a regulatory circuit between NH4+ and auxin signaling that functions in root development in rice.

Closely-located transposable elements (TEs) can induce chromosomal breakage and rearrangements via alternative transposition (AT) reactions. Our previous study showed that diverse chromosomal rearrangements were induced by two inversely-oriented Ds elements at the OsRLG5 (Oryza sativa receptor-like kinase gene 5) locus in regenerated rice plants. Here, several novel chromosomal rearrangements were identified in a population of tissue culture regenerants, and their proposed Ac/Ds-transposition mechanisms were discussed. In the first type of event, AT was induced by the same Ds element on each of two sister chromatids and resulted in the inversion of genomic DNA flanking the Ds element. In the second type of event, DNA segments of the inter-transposon segment (ITS) region were deleted or inverted. This novel local rearrangement likely resulted from an AT reaction of two directly-oriented Ds elements located on the same chromatid. The 5' and 3' termini of two Ds elements were re-inserted into two different sites inside the ITS, which generated the subsequent deletion and inversion. In the third type of event, two inversely-oriented Ds elements induced homologous recombination and chromosomal translocation. Together, these results showed the diversity of Ac/Ds-mediated chromosomal rearrangements and demonstrated the utility of the experimental system for examining the mechanisms underlying Ac/Ds AT reactions.

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a significant pest in soybean-growing regions and is native to eastern Asia. The life cycle of the aphid is complex with different physical forms and two types of host plants that are targeted. The winged females are produced on buckthorn (Rhamnus spp.) in the spring and migrate into the soybean fields approximately 2 weeks before the soybeans emerge. This phenomenon suggests that A. glycines could infest other hosts (transitional hosts) during the period before soybean emergence. To verify the availability of transitional hosts, eggs of aphids were collected from Rhamnus davurica Pallus (Rhamnales: Rhamnaceae), the hatched aphids were reared, and the subsequent winged generation was transferred onto several candidate hosts. The possible transitional hosts of A. glycines were Capsella bursa-pastoris (L.) Medic (Capparales: Brassicaceae), Metaplexis japonica (Thunb.) Makino (Gentianales: Asclepiadaceae), and Artemisia scoparia Waldst. et Kit (Asterales: Compositae). The aphids found on M. japonica were identified as A. glycines, and the aphids found on the other hosts were identified as the cotton aphid, Aphis gossypii Glover. Thus, M. japonica is likely the transitional host of A. glycines.

OSH6 (Oryza sativa Homeobox6) is an ortholog of lg3 (Liguleless3) in maize. We generated a novel allele, termed OSH6-Ds, by inserting a defective Ds element into the third exon of OSH6, which resulted in a truncated OSH6 mRNA. The truncated mRNA was expressed ectopically in leaf tissues and encoded the N-terminal region of OSH6, which includes the KNOX1 and partial KNOX2 subdomains. This recessive mutant showed outgrowth of bracts or produced leaves at the basal node of the panicle. These phenotypes distinguished it from the OSH6 transgene whose ectopic expression led to a "blade to sheath transformation" phenotype at the midrib region of leaves, similar to that seen in dominant Lg3 mutants. Expression of a similar truncated OSH6 cDNA from the 35S promoter (35S::DeltaOSH6) confirmed that the ectopic expression of this product was responsible for the aberrant bract development. These data suggest that OSH6-Ds interferes with a developmental mechanism involved in bract differentiation, especially at the basal nodes of panicles.

Insertional mutagen-mediated gene tagging populations have been essential resources for analyzing the function of plant genes. In rice, maize transposable elements have been successfully utilized to produce transposant populations. However, many generations and substantial field space are required to obtain a sufficiently sized transposant population. In rice, the japonica and indica subspecies are phenotypically and genetically divergent. Here, callus cultures with seeds carrying Ac and Ds were used to produce 89,700 lines of Dongjin, a japonica cultivar, and 6,200 lines of MGRI079, whose genome is composed of a mixture of the genetic backgrounds of japonica and indica. Of the more than 3,000 lines examined, 67% had Ds elements. Among the Ds-carrying lines, 81% of Dongjin and 63% of MGRI079 contained transposed Ds, with an average of around 2.0 copies. By examining more than 15,000 lines, it was found that 12% expressed the reporter gene GUS during the early-seedling stage. GUS was expressed in root hairs and crown root initials at estimated frequencies of 0.78% and 0.34%, respectively. The 5,271 analyzed Ds loci were found to be randomly distributed over all of the rice chromosomes.

Background N-ethyl-maleimide sensitive factor adaptor protein receptor (SNAREs) domain-containing proteins were known as key players in vesicle-associated membrane fusion. Genetic screening has revealed the function of SNAREs in different aspects of plant biology, but the role of many SNAREs are still unknown. In this study, we have characterized the role of Arabidopsis Qc-SNARE protein AtBS14b in brassinosteroids (BRs) signaling pathway. Results AtBS14b overexpression (AtBS14b ox) plants exhibited short hypocotyl and petioles lengths as well as insensitivity to exogenously supplied BR, while AtBS14b mutants did not show any visible BR-dependent morphological differences. BR biosynthesis enzyme BR6OX2 expression was slightly lower in AtBS14b ox than in wild type plants. Further BR-mediated repression of BR6OX2, CPD and DWF4 was inhibited in AtBS14b ox plants. AtBS14b-mCherry fusion protein localized in vesicular compartments surrounding plasma membrane in N. benthamiana leaves. In addition, isolation of AtBS14b-interacting BR signaling protein, which localized in plasma membrane, showed that AtBS14b directly interacted with membrane steroid binding protein 1 (MSBP1), but did not interact with BAK1 or BRI1. Conclusion These data suggested that Qc-SNARE protein AtBS14b is the first SNARE protein identified that interacts with MSBP1, and the overexpression of AtBS14b modulates BR response in Arabidopsis.