Rice copine genes OsBON1 and OsBON3 function as suppressors of broad‐spectrum disease resistance

Breeding for disease resistance is the most effective strategy to control diseases, particularly with broad‐spectrum disease resistance in many crops. However, knowledge on genes and mechanism of broad‐spectrum resistance and trade‐off between defence and growth in crops is limited. Here, we show that the rice copine genes OsBON1 and OsBON3 are critical suppressors of immunity. Both OsBON1 and OsBON3 changed their protein subcellular localization upon pathogen challenge. Knockdown of OsBON1 and dominant negative mutant of OsBON3 each enhanced resistance to rice bacterial and fungal pathogens with either hemibiotrophic or necrotrophic lifestyles. The defence activation in OsBON1 knockdown mutants was associated with reduced growth, both of which were largely suppressed under high temperature. In contrast, overexpression of OsBON1 or OsBON3 decreased disease resistance and promoted plant growth. However, neither OsBON1 nor OsBON3 could rescue the dwarf phenotype of the Arabidopsis BON1 knockout mutant, suggesting a divergence of the rice and Arabidopsis copine genes. Our study therefore shows that the rice copine genes play a negative role in regulating disease resistance and their expression level and protein location likely have a large impact on the balance between immunity and agronomic traits.     

ROS and trehalose regulate sclerotial development in Rhizoctonia solani AG-1 IA

Rhizoctonia solani AG-1 IA is the causal agent of rice sheath blight (RSB) and causes severe economic losses in rice-growing regions around the world. The sclerotia play an important role in the disease cycle of RSB. In this study, we report the effects of reactive oxygen species (ROS) and trehalose on the sclerotial development of R. solani AG-1 IA. Correlation was found between the level of ROS in R. solani AG-1 IA and sclerotial development. Moreover, we have shown the change of ROS-related enzymatic activities and oxidative burst occurs at the sclerotial initial stage. Six genes related to the ROS scavenging system were quantified in different sclerotial development stages by using quantitative RT-PCR technique, thereby confirming differential gene expression. Fluorescence microscopy analysis of ROS content in mycelia revealed that ROS were predominantly produced at the hyphal branches during the sclerotial initial stage. Furthermore, exogenous trehalose had a significant inhibitory effect on the activities of ROS-related enzymes and oxidative burst and led to a reduction in sclerotial dry weight. Taken together, the findings suggest that ROS has a promoting effect on the development of sclerotia, whereas trehalose serves as an inhibiting factor to sclerotial development in R. solani AG-1 IA.     

培养条件下发菜细胞超微结构的观察

通过观察发菜(Nostoc flagelliforme Born.et Flah.)细胞在不同生长条件的超微结构,探讨细胞的生长和发育特点以及胶质鞘的形成规律。在蒸馏水中浸泡2h后,各种细胞代谢活跃,能进行正常的生长和分裂,其中营养细胞的细胞壁以及一特殊类型的大细胞与胶质鞘的形成有关。在pH7.0的培养液中,出现与胶质鞘有关的细胞结构。在酸性培养液中未见这些结构。在不合适的pH条件下,一特殊类型的小细胞大量增殖。     

CULTURE OF THE TERRESTRIAL CYANOBACTERIUM,NOSTOC FLAGELLIFORME (CYANOPHYCEAE), UNDER AQUATIC CONDITIONS1

Both colonies and free‐living cells of the terrestrial cyanobacterium, Nostoc flagelliforme (Berk. & Curtis) Bornet & Flahault, were cultured under aquatic conditions to develop the techniques for the cultivation and restoration of this endangered resource. The colonial filaments disintegrated with their sheaths ruptured in about 2 days without any desiccating treatments. Periodic desiccation played an important role in preventing the alga from decomposing, with greater delays to sheath rupture with a higher frequency of exposure to air. The bacterial numbers in the culture treated with seven periods of desiccation per day were about 50% less compared with the cultures without the desiccation treatment. When bacteria in the culture were controlled, the colonial filaments did not disintegrate and maintained the integrity of their sheath for about 20 days even without the desiccation treatments, indicating the importance of desiccation for N. flagelliforme to prevent them from being disintegrated by bacteria. On the other hand, when free‐living cells obtained from crushed colonial filaments were cultured in liquid medium, they developed into single filaments with sheaths, within which multiple filaments were formed later on as a colony. Such colonial filaments were developed at 15, 25, and 30° C at either 20 or 60 μmol photons·m^?2·s^?1; colonies did not develop at 180 μmol photons·m^?2·s^?1, though this light level resulted in the most rapid growth of the cells. Conditions of 60 μmol photons·m^?2·s^?1 and 25° C appeared to result in the best colonial development and faster growth of the sheath‐held colonies of N. flagelliforme when cultured indoor under aquatic conditions.     

Grasshoppers efficiently process C4 grass leaf tissues: implications for patterns of host-plant utilization

Leaf‐chewing insects are commonly believed to be unable to crush the nutrient‐rich bundle sheath cells (BSC) of C₄ grasses. This physical constraint on digestion is thought to reduce the nutritional quality of these grasses substantially. However, recent evidence suggests that BSC are digested by grasshoppers. To directly assess the ability of grasshoppers to digest C₄ grass BSC, leaf particles of Bouteloua curtipendula (Poaceae) were examined from the digestive tracts of two grasshopper species: Camnula pellucida (Scudder) (primarily a grass feeder) and Melanoplus sanguinipes (Fabricius) (a forb and grass generalist) (Orthoptera: Acrididae). Transmission electron microscopy was used to make the first observations of BSC crushing by herbivorous insects. Camnula pellucida and M. sanguinipes crushed over 58% and 24%, respectively, of the BSC in ingested leaf tissues. In addition, chloroplast and cell membranes were commonly disrupted in uncrushed BSC, permitting soluble nutrients to be extracted, even when BSC walls remain intact. The greater efficiency with which C. pellucida crushes BSC is consistent with the idea that grass‐feeding species are better adapted for handling grass leaf tissues than are generalist species. By demonstrating the effectiveness with which the BSC of B. curtipendula can be crushed and extracted by both species of grasshoppers, this study suggests one reason why C₄ grasses are not generally avoided by grasshoppers: at least some C₄ grasses can be more easily digested than has been hypothesized.     

High spatial resolution mass spectrometry imaging reveals the genetically programmed,developmental modification of the distribution of thylakoid membrane lipids among individual cells of maize leaf

Metabolism in plants is compartmentalized among different tissues, cells and subcellular organelles. Mass spectrometry imaging (MSI) with matrix‐assisted laser desorption ionization (MALDI) has recently advanced to allow for the visualization of metabolites at single‐cell resolution. Here we applied 5‐ and 10 μm high spatial resolution MALDI‐MSI to the asymmetric Kranz anatomy of Zea mays (maize) leaves to study the differential localization of two major anionic lipids in thylakoid membranes, sulfoquinovosyldiacylglycerols (SQDG) and phosphatidylglycerols (PG). The quantification and localization of SQDG and PG molecular species, among mesophyll (M) and bundle sheath (BS) cells, are compared across the leaf developmental gradient from four maize genotypes (the inbreds B73 and Mo17, and the reciprocal hybrids B73 × Mo17 and Mo17 × B73). SQDG species are uniformly distributed in both photosynthetic cell types, regardless of leaf development or genotype; however, PG shows photosynthetic cell‐specific differential localization depending on the genotype and the fatty acyl chain constituent. Overall, 16:1‐containing PGs primarily contribute to the thylakoid membranes of M cells, whereas BS chloroplasts are mostly composed of 16:0‐containing PGs. Furthermore, PG 32:0 shows genotype‐specific differences in cellular distribution, with preferential localization in BS cells for B73, but more uniform distribution between BS and M cells in Mo17. Maternal inheritance is exhibited within the hybrids, such that the localization of PG 32:0 in B73 × Mo17 is similar to the distribution in the B73 parental inbred, whereas that of Mo17 × B73 resembles the Mo17 parent. This study demonstrates the power of MALDI‐MSI to reveal unprecedented insights on metabolic outcomes in multicellular organisms at single‐cell resolution.     

Overexpression of Jatropha curcas Defensin (JcDef) Enhances Sheath Blight Disease Resistance in Tobacco

Plant defensins are small, basic, cysteine‐rich peptides, belonging to the antimicrobial peptide superfamily, commonly found in the plant kingdom. In this study, we cloned and characterized a plant defensin gene from Jatropha curcas (JcDef). JcDef carried conserved receptor binding sites and a cysteine motif, and it was phylogenetically grouped together with defensin Ec‐AMP‐D2‐like in Elaeis guineensis. JcDef is localized to cytoplasm and highly expressed in young tissues with fast metabolism such as cotyledons and stem apexes. Transgenic expression of JcDef in tobacco showed enhanced resistance against sheath blight disease caused by R. solani, indicating the antibacterial function.     

Infection process of Gaeumannomyces graminis var. graminis on the roots and culms of rice

Crown sheath rot, caused by the ascomycete Gaeumannomyces graminis var. graminis that infects the root and the base of the culm of rice, causes early grains maturation, tiller death and reduced yield. As a paucity of information exists in the literature on the rice‐G. graminis var. graminis interaction at the microscopic level, this study aimed to gain novel insights into the infection process of this pathogen in the root and culm of rice using both light and scanning electron microscopy. In the roots, the fungus initially colonized the epidermal, exodermal and sclerenchyma cells. At 15 days after inoculation (dai), fungal hyphae colonized the cortex and clusters of perithecia were observed in the roots. At 20 dai, the fungus reached the central cylinder, and an intense fungal colonization at the base of the culm was observed that resulted in the formation of a mycelial mat on both adaxial and abaxial surfaces of the leaf sheaths. At 25 dai, fungal growth was noticed in the parenchyma cells, vascular bundles and airspaces. Perithecia emerged through the base of prophyllum and from the first leaf sheath at 30 dai. The results of this study provide new insights into the infection process of G. graminis var. graminis in rice and may help to find better control measures in reducing crown sheath rot development.     

The tail sheath structure of bacteriophage T4: a molecular machine for infecting bacteria

The contractile tail of bacteriophage T4 is a molecular machine that facilitates very high viral infection efficiency. Its major component is a tail sheath, which contracts during infection to less than half of its initial length. The sheath consists of 138 copies of the tail sheath protein, gene product (gp) 18, which surrounds the central non‐contractile tail tube. The contraction of the sheath drives the tail tube through the outer membrane, creating a channel for the viral genome delivery. A crystal structure of about three quarters of gp18 has been determined and was fitted into cryo‐electron microscopy reconstructions of the tail sheath before and after contraction. It was shown that during contraction, gp18 subunits slide over each other with no apparent change in their structure.