Effects of Eupatorium yellow vein virus infection on photosynthetic rate, chlorophyll content and chloroplast structure in leaves of Eupatorium makinoi during leaf development

Urdbean Leaf Crinkle Virus: A Mystery Waiting to Be Solved

Urdbean leaf crinkle disease (ULCD) affects mainly the urdbean or blackgram (Vigna mungo (L.) Hepper) causing distinct symptoms that often result in serious yield losses. It has been known to occur for more than five decades and is considered to be of viral etiology. The identity of the causal agent, often referred to as the urdbean leaf crinkle virus, is not unequivocally proved. There are few attempts to characterize the causal agent of ULCD; however, there is no unanimity in the results. Recent attempts to characterize the causal agent of ULCD using next-generation sequencing of the virome of ULCD-affected urdbean plants indicated the involvement of cowpea mild mottle virus; however, without conforming through Koch's postulates, the etiology of ULCD remains inconclusive. Claims of different insect vectors involved in the transmission of ULCD make this disease even more mysterious. The information available so far indicates that either two different viruses are causing ULCD or a mixture of viruses is involved. The identity of the virus/es causing ULCD still remains to be unambiguously ascertained. In this review, we attempt to analyze information on the various aspects of ULCD.

Untangling the Physio-Chemical and Transcriptional Changes of Black Gram Cultivars After Infection With Urdbean Leaf Crinkle Virus

Black gram (Vigna mungo) is an important pulse crop of India. The leaf crinkle disease caused by the urdbean leaf crinkle virus (ULCV) is a severe threat to black gram production. Black gram plants infected by ULCV show a considerable decline in plant growth and yield. However, detailed information about the interactions between the host, black gram, and ULCV is unclear. This study investigated the responses of two cultivars VBN (Bg) 6 and CO 5 to ULCV infection by physiological, biochemical, and transcriptional analyses. Virus symptoms were mild in VBN (Bg) 6 but were serious in CO 5. Upon the viral infection, VBN (Bg) 6 exhibited a low reduction in chlorophyll content than CO 5. The levels of sugar, protein, phenol, hydrogen peroxide (H2O2), and malondialdehyde (MDA) contents were altered by a viral infection in both cultivars. Although, the activities of antioxidant enzymes [Ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)] were increased by ULCV infection. Following the viral infection, the expression level of the salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) defense pathway-related genes was recorded higher in the VBN (Bg) 6 than that recorded in CO 5, indicating a positive correlation between resistance and these indicative indices. This dynamic physio-biochemical and transcriptional profiles of two black gram cultivars on ULCV infection augment our understanding of the complex interaction response between this crop and its pathogen. Additionally, it offers an inventory of potential indicators for future black gram screening and breeding to enhance resistance.

Photosynthetic and Growth Responses in a Pioneer Tree (Japanese White Birch) and Competitive Perennial Weeds (Eupatorium sp.) Grown Under Different Regimes With Limited Water Supply to Waterlogging

For a successful natural regeneration of Japanese white birch (Betula platyphylla var. japonica), competitive vegetation should be managed. Here, we clarified how soil water condition modifies the competitiveness of Japanese white birch against perennial weeds, Eupatorium species, based on an ecophysiological approach combining a glasshouse experiment and a field survey. We investigated photosynthetic and growth responses to various water regimes from water deficit to waterlogging (two times-a-week irrigation, three times-a-week irrigation, half waterlogging, and full waterlogging) in pot-grown seedlings of Japanese white birch and the competitive weed Eupatorium makinoi. The ratio of seedling height of Japanese white birch to seedling height of E. makinoi showed a decreasing trend from two times-a-week irrigation to full waterlogging, which suggests a lower competitiveness for light resource in Japanese white birch with increasing soil wetness. The maximum rate of Rubisco carboxylation (Vc,max) based on unit N was lower in waterlogging treatments than in two times- and three times-a-week irrigation in Japanese white birch, whereas E. makinoi showed the opposite response. This suggests that N partitioning into Rubisco and/or Rubisco activation might be suppressed in Japanese white birch but enhanced in E. makinoi under waterlogging. The maximum photochemical efficiency of photosystem II (Fv/Fm) was also lower in seedlings of Japanese white birch grown under waterlogging treatments. We further conducted a field survey on the relationship between Fv/Fm and topographic wetness index (TWI) in seedlings of Japanese white birch and E. glehnii (closely related to E. makinoi) naturally grown in a study site 5 years after canopy tree cutting. Lower Fv/Fm was observed in seedlings of Japanese white birch with increasing TWI, whereas no significant trend was observed in E. glehnii, in agreement with the glasshouse experiment. Thus, keeping soils not always humid might be favorable to photosynthetic performance and growth competitive ability of Japanese white birch against Eupatorium species.

Tomato Yellow Leaf Curl China Virus Impairs Photosynthesis in the Infected Nicotiana benthamiana with βC1 as an Aggravating Factor

Tomato yellow leaf curl China virus is a species of the widespread geminiviruses. The infection of Nicotiana benthamiana by Tomato yellow leaf curl China virus (TYLCCNV) causes a reduction in photosynthetic activity, which is part of the viral symptoms. βC1 is a viral factor encoded by the betasatellite DNA (DNAβ) accompanying TYLCCNV. It is a major viral pathogenicity factor of TYLCCNV. To elucidate the effect of βC1 on plants' photosynthesis, we measured the relative chlorophyll (Chl) content and Chl fluorescence in TYLCCNV-infected and βC1 transgenic N. benthamiana plants. The results showed that Chl content is reduced in TYLCCNV A-infected, TYLCCNV A plus DNAβ (TYLCCNV A + β)-infected and βC1 transgenic plants. Further, changes in Chl fluorescence parameters, such as electron transport rate, F v /F m , NPQ, and qP, revealed that photosynthetic efficiency is compromised in the aforementioned N. benthamiana plants. The presense of βC1 aggravated the decrease of Chl content and photosynthetic efficiency during viral infection. Additionally, the real-time quantitative PCR analysis of oxygen evolving complex genes in photosystem II, such as PsbO, PsbP, PsbQ, and PsbR, showed a significant reduction of the relative expression of these genes at the late stage of TYLCCNV A + β infection and at the vegetative stage of βC1 transgenic N. benthamiana plants. In summary, this study revealed the pathogenicity of TYLCCNV in photosynthesis and disclosed the effect of βC1 in exacerbating the damage in photosynthesis efficiency by TYLCCNV infection.

Deletion of ptn1, a PTEN/TEP1 Orthologue, in Ustilago maydis Reduces Pathogenicity and Teliospore Development

The PTEN/PI3K/mTOR signal transduction pathway is involved in the regulation of biological processes such as metabolism, cell growth, cell proliferation, and apoptosis. This pathway has been extensively studied in mammals, leading to the conclusion that PTEN is a major tumor suppressor gene. PTEN orthologues have been characterized in a variety of organisms, both vertebrates and non-vertebrates, and studies of the associated PTEN/PI3K/mTOR pathway indicate that it is widely conserved. Studies in fungal systems indicated a role of PTEN in fungal defense mechanisms in Candida albicans, and in the developmental process of sporulation in Saccharomyces cerevisiae. The present study was aimed at investigating the role of the PTEN ortholog, ptn1, in Ustilago maydis, the pathogen of maize. U. maydis ptn1 mutant strains where ptn1 gene is deleted or overexpressed were examined for phenotypes associate with mating, virulence and spore formation. While the overexpression of ptn1 had no substantial effects on virulence, ptn1 deletion strains showed slight reductions in mating efficiency and significant reductions in virulence; tumor formation on stem and/or leaves were severely reduced. Moreover, tumors, when present, had significantly lower levels of mature teliospores, and the percent germination of such spores was similarly reduced. Thus, ptn1 is required for these important aspects of virulence in this fungus.

Agronomical, biochemical and histological response of resistant and susceptible wheat and barley under BYDV stress

Barley yellow dwarf virus-PAV (BYDV-PAV) is one of the major viruses causing a widespread and serious viral disease affecting cereal crops. To gain a better understanding of plant defence mechanisms of BYDV resistance genes (Bdv2 and RYd2) against BYDV-PAV infection, the differences in agronomical, biochemical and histological changes between susceptible and resistant wheat and barley cultivars were investigated. We found that root growth and total dry matter of susceptible cultivars showed greater reduction than that of resistant ones after infection. BYDV infected leaves in susceptible wheat and barley cultivars showed a significant reduction in photosynthetic pigments, an increase in the concentration of reducing sugar. The protein levels were also low in infected leaves. There was a significant increase in total phenol contents in resistant cultivars, which might reflect a protective mechanism of plants against virus infection. In phloem tissue, sieve elements (SE) and companion cells (CC) were severely damaged in susceptible cultivars after infection. It is suggested that restriction of viral movement in the phloem tissue and increased production of phenolic compounds may play a role in the resistance and defensive mechanisms of both Bdv2 and RYd2 against virus infection.

Why mosaic? Gene expression profiling of African cassava mosaic virus-infected cassava reveals the effect of chlorophyll degradation on symptom development

Cassava mosaic disease, caused by cassava begomoviruses, is the most serious disease for cassava in Africa. However, the pathogenesis of this disease is poorly understood. We employed high throughput digital gene expression profiling based on the Illumina Solexa sequencing technology to investigate the global transcriptional response of cassava to African cassava mosaic virus infection. We found that 3,210 genes were differentially expressed in virus-infected cassava leaves. Gene ontology term and Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that genes implicated in photosynthesis were most affected, consistent with the chlorotic symptoms observed in infected leaves. The upregulation of chlorophyll degradation genes, including the genes encoding chlorophyllase, pheophytinase, and pheophorbide a oxygenase, and downregulation of genes encoding the major apoproteins in light-harvesting complex II were confirmed by qRT-PCR. These findings, together with the reduction of chlorophyll b content and fewer grana stacks in the infected leaf cells, reveal that the degradation of chlorophyll plays an important role in African cassava mosaic virus symptom development. This study will provide a road map for future investigations into viral pathogenesis.

Effects of cucumber mosaic virus infection on electron transport and antioxidant system in chloroplasts and mitochondria of cucumber and tomato leaves

We examined the responses of the photosynthetic and respiratory electron transport and antioxidant systems in cell organelles of cucumber (Cucumis sativus L.) and tomato (Lycopersicon esculentum Mill.) leaves to infection of cucumber mosaic virus (CMV) by comparing the gas exchange, Chl fluorescence, respiratory electron transport, superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate-glutathione (AsA-GSH) cycle enzymes and the production of H(2)O(2) in chloroplasts, mitochondria and soluble fraction in virus-infected and non-infected leaves. Long-term CMV infection resulted in decreased photosynthesis and respiration rates. Photosynthetic electron flux to carbon reduction, respiratory electron transport via both complex I and complex II and also the Cyt respiration rate all significantly decreased, while photosynthetic alternative electron flux and alternative respiration significantly increased. These changes in electron transport were accompanied by a general increase in the activities of SOD/AsA-GSH cycle enzymes followed by an increased H(2)O(2) accumulation in chloroplasts and mitochondria. These results demonstrated that disturbance of photosynthetic and respiratory electron transport by CMV also affected the antioxidative systems, thereby leading to oxidative stress in various organelles.

Impairment of leaf hydraulics in young plants of Citrus aurantium (sour orange) infected by Phoma tracheiphila

Phoma trachephila (Petri) Kantschaveli et Gikachvili causes dieback of several Citrus species. The impact of this fungus on leaf hydraulics was studied in Citrus aurantium L. (sour orange) with the aim of identifying the primary mechanism of damage to leaves. Leaves inoculated with a conidial suspension were measured for conductance to water vapor (g_L) and specific hydraulic conductance (K_leaf) every 3 days after inoculation. The earliest symptom of infection consisted of vein chlorosis. Functional vein density (FVD) was monitored and microscopic observations were made of major vein conduits. Impairment of vein hydraulics started 25 days after inoculation with a losses of K_leaf of 40% and g_L of ~60%. Most minor veins within chlorotic areas were no longer functioning and some conduits of the major veins showed digested interconduit pits leading to vein cavitation. The close K_leaf-FVD relationship revealed that vein impairment caused drop of K_leaf and, consequently, of g_L at chlorotic areas. Leaf infection was focused to veins that were first forced to embolise and then invaded by fungal hyphae. The vein embolism due to the Phoma amplifies the native dominant hydraulic resistance of leaf veins, and leads ultimately to early shedding of infected leaves.