Characterization and primary functional analysis of a bamboo NAC gene targeted by miR164b

Key message

PeSNAC1 , a stress-related NAC1 from Phyllostachys edulis , was characterized. Ectopic expression in Arabidopsis indicated that PeSNAC1 together with ped -miR164b participated in the regulation of organ boundaries and stress tolerance.

Abstract

NAC (NAM, ATAF1/2 and CUC2) participates in many different processes regulating plant growth, development, and stress response. A total of 125 NAC genes have been predicted in moso bamboo (Phyllostachys edulis), but their roles are poorly understood. PeSNAC1 targeted by ped-miR164b was focused for further study. The cleavage of PeSNAC1 mRNA guided by ped-miR164b was validated using RLM-5′ RACE. Tissue-specific expression analysis demonstrated that ped-miR164b had a declining trend from root, sheath, leaf, to that of stem, which was opposite to that of PeSNAC1. Transgenic Arabidopsis plants overexpressing either PeSNAC1 (OX-PeSNAC1) or, ped-miR164b (OX-ped-miR164b) driven by the CaMV35S promoter were generated. OX-ped-miR164b plants showed similar phenotype of cuc2 mutants whose growth was seriously suppressed. Compared with Col-0, sense OX-PeSNAC1 plants grew rapidly and flowered earlier, whereas antisense plants grew slowly and exhibited delayed flowering. Sense OX-PeSNAC1 plants had the greatest number of lateral roots, while antisense OX-PeSNAC1 and OX-ped-miR164b plants had fewer lateral roots than Col-0. Under NaCl and PEG6000 stresses, survival rates were higher and F _v/F _m values declined more slowly in sense OX-PeSNAC1 plants than in Col-0, with lower survival rates and a more rapid decrease in F _v/F _m values conversely observed in antisense OX-PeSNAC1 and OX-ped-miR164b plants. These findings indicated that ped-miR164b-targeted PeSNAC1 may play key roles in plant development and tolerance to salinity and drought stresses.

     

Biodiversity of arbuscular mycorrhizal fungi in the drawdown zone of the Three Gorges Reservoir under different fertilization histories

Impoundment of the Three Gorges Reservoir (TGR) has dramatically influenced the riparian environment and shaped a new drawdown zone, which has experienced long-term winter conditions and short periods of summer flooding. The community structure and diversity of arbuscular mycorrhizal (AM) fungi (AMF) were investigated in three areas with different fertilization histories [Area A (5 years of fertilization), Area B (3 years of fertilization) and Area C (no fertilization)] in the drawdown zone of the TGR. Altogether, 50 AMF species were identified; the genera Acaulospora, Funneliformis and Glomus were predominant. The AM fungal community differed among areas A, B and C. A higher isolation frequency and relative abundance of Acaulospora, Ambispora, Entrophospora and Paraglomus were observed in areas A and B; however, Claroideoglomus, Diversispora, Sclerocystis and Septoglomus were more abundant in Area C. The highest spore density occurred in Area C, and was slightly lower in Area A and lowest in Area B. Conversely, species richness and diversity indices (Shannon–Wiener and evenness indices) were the highest in Area A, followed by areas C and B. Based on nonmetric multidimensional scaling analyses, the distribution of AMF was influenced by plant host, fertilization practice and environmental factors. Among them, the soil physicochemical properties were the main drivers affecting AMF, in which three edaphic attributes (carbon/nitrogen ratio, available phosphorus and potassium content) were significantly correlated (P < 0.001) with the AM fungal community composition in the three areas of the drawdown zone of the TGR.     

Structural Correlation of the Neck Coil with the Coiled-coil (CC1)-Forkhead-associated (FHA) Tandem for Active Kinesin-3 KIF13A

Processive kinesin motors often contain a coiled-coil neck that controls the directionality and processivity. However, the neck coil (NC) of kinesin-3 is too short to form a stable coiled-coil dimer. Here, we found that the coiled-coil (CC1)-forkhead-associated (FHA) tandem (that is connected to NC by Pro-390) of kinesin-3 KIF13A assembles as an extended dimer. With the removal of Pro-390, the NC-CC1 tandem of KIF13A unexpectedly forms a continuous coiled-coil dimer that can be well aligned into the CC1-FHA dimer. The reverse introduction of Pro-390 breaks the NC-CC1 coiled-coil dimer but provides the intrinsic flexibility to couple NC with the CC1-FHA tandem. Mutations of either NC, CC1, or the FHA domain all significantly impaired the motor activity. Thus, the three elements within the NC-CC1-FHA tandem of KIF13A are structurally interrelated to form a stable dimer for activating the motor. This work also provides the first direct structural evidence to support the formation of a coiled-coil neck by the short characteristic neck domain of kinesin-3.     

Comparison of ultrastructural and physiological changes of potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) plantlets subjected to salt and modeling drought stresses

Salinity and drought are two severe abiotic stresses that affect plant growth and decrease food production worldwide. Compared to the field plants, test-tube plantlets could be more direct and fast to investigate the mechanism of stress adaptation. In the present study, the ultrastructural and physiological differences of potato (Solanum tuberosum L. c.v. “Longshu No. 3”) plantlets in response to the gradient saline (0, 25, 50, 100, and 200 mM NaCl) and the modeling drought stresses with polyethylene glycol (PEG) at the concentrations of 0, 2, 4, 6, and 8 % were analyzed. The results show that the severe salt (200 mM NaCl) and the modeling drought stresses (8 % PEG) inhibited the plantlet growth. There are considerable differences in their ultrastructural alteration under salt and modeling drought adaptation: PEG caused the increase in the number of stacked chloroplast, plastoglobuli, and starch; NaCl induced the decrease in the number of chloroplast and plastoglobuli. Moreover, plantlet has higher free proline content, less malondialdehyde (MDA) content, and higher activities of catalase (CAT) and superoxide dismutase (SOD) under the gradient NaCl treatments than the gradient PEG treatments. The results of this study will provide theoretical and practical insights into characterizing the ultrastructural and physiological differences of plants adapting to various stressful environments.     

Variation in circadian rhythms is maintained among and within populations in Boechera stricta

Circadian clocks have evolved independently in all three domains of life, and fitness benefits of a functional clock have been demonstrated in experimental genotypes in controlled conditions. Still, little is known about genetic variation in the clock and its fitness consequences in natural populations from heterogeneous environments. Using Wyoming populations of the Arabidopsis relative Boechera stricta as our study system, we demonstrate that genetic variation in the clock can occur at multiple levels: means of circadian period among populations sampled at different elevations differed by less than 1 h, but means among families sampled within populations varied by as much as 3.5 h. Growth traits also varied among and within populations. Within the population with the most circadian variation, we observed evidence for a positive correlation between period and growth and a negative correlation between period and root‐to‐shoot ratio. We then tested whether performance tradeoffs existed among families of this population across simulated seasonal settings. Growth rankings of families were similar across seasonal environments, but for root‐to‐shoot ratio, genotype × environment interactions contributed significantly to total variation. Therefore, further experiments are needed to identify evolutionary mechanisms that preserve substantial quantitative genetic diversity in the clock in this and other species.     

A conserved pattern in plant‐mediated interactions between herbivores

Plant‐mediated interactions between herbivores are important determinants of community structure and plant performance in natural and agricultural systems. Current research suggests that the outcome of the interactions is determined by herbivore and plant identity, which may result in stochastic patterns that impede adaptive evolution and agricultural exploitation. However, few studies have systemically investigated specificity versus general patterns in a given plant system by varying the identity of all involved players. We investigated the influence of herbivore identity and plant genotype on the interaction between leaf‐chewing and root‐feeding herbivores in maize using a partial factorial design. We assessed the influence of leaf induction by oral secretions of six different chewing herbivores on the response of nine different maize genotypes and three different root feeders. Contrary to our expectations, we found a highly conserved pattern across all three dimensions of specificity: The majority of leaf herbivores elicited a negative behavioral response from the different root feeders in the large majority of tested plant genotypes. No facilitation was observed in any of the treatment combinations. However, the oral secretions of one leaf feeder and the responses of two maize genotypes did not elicit a response from a root‐feeding herbivore. Together, these results suggest that plant‐mediated interactions in the investigated system follow a general pattern, but that a degree of specificity is nevertheless present. Our study shows that within a given plant species, plant‐mediated interactions between herbivores of the same feeding guild can be stable. This stability opens up the possibility of adaptations by associated organisms and suggests that plant‐mediated interactions may contribute more strongly to evolutionary dynamics in terrestrial (agro)ecosystems than previously assumed.