Search

Phytoplasmas are a threat to cassava production, but have not been found from cassava in Japan. Here, we present the discovery of phytoplasma in asymptomatic plants propagated in Japan. A 16S rRNA gene sequence analysis showed that the phytoplasma was related to ‘Candidatus Phytoplasma pruni’. Analyses based on 16S rRNA, secY, and ribosomal protein gene sequences revealed that the phytoplasma was closely related to phytoplasmas found in cassava in Latin America. Infected plants remained asymptomatic during cultivation for more than 11 months. This is the first molecular evidence of phytoplasma infection in cassava in Japan. [ABSTRACT FROM AUTHOR]

Deregulated expression of an Arabidopsis H/Ca antiporter (sCAX1) in agricultural crops increases total calcium (Ca) but may result in yield losses due to Ca deficiency-like symptoms. Here we demonstrate that co-expression of a maize calreticulin (CRT, a Ca binding protein located at endoplasmic reticulum) in sCAX1-expressing tobacco and tomato plants mitigated these adverse effects while maintaining enhanced Ca content. Co-expression of CRT and sCAX1 could alleviate the hypersensitivity to ion imbalance in tobacco plants. Furthermore, blossom-end rot (BER) in tomato may be linked to changes in CAX activity and enhanced CRT expression mitigated BER in sCAX1 expressing lines. These findings suggest that co-expressing Ca transporters and binding proteins at different intracellular compartments can alter the content and distribution of Ca within the plant matrix. [ABSTRACT FROM AUTHOR]

Bottle gourd ( Lagenaria siceraria Standl.) has been commonly used as a source of rootstock for watermelon. To improve its performance as a rootstock without adverse effects on the scion, the bottle gourd was genetically engineered using a modified Arabidopsis Ca2+/H+ exchanger sCAX2B. This transporter provides enhanced Ca2+ substrate specificity and decreased Mn2+ transport capability. Our previous work demonstrated that s CAX2B bottle gourds were more robust and nutrient dense than controls. Here, several cucurbit crops were test-grafted onto the transgenic bottle gourd to determine its effect on the scions. The grafted watermelons and melons onto the transgenic rootstocks appeared to show more robust growth than the controls 35 days after greenhouse transplanting. Watermelon fruits with the watermelon/transgenic bottle gourd (scion/rootstock) combination demonstrated higher osmotic pressure and more soluble solids than controls. These results suggest that s CAX2B expression in the bottle gourd rootstock facilitates improved watermelon quality through the translocation of nutrients and/or water toward enhancing the biomass of scion. [ABSTRACT FROM AUTHOR]

Ca2+ levels in plants are controlled in part by H+/Ca2+ exchangers. Structure/function analysis of the Arabidopsis H+/cation exchanger, CAX1, revealed that a nine amino acid region (87–95) is involved in CAX1-mediated Ca2+ specificity. CAX3 is 77% identical (93% similar) to CAX1, and when expressed in yeast, localizes to the vacuole but does not suppress yeast mutants defective in vacuolar Ca2+ transport. Transgenic tobacco plants expressing CAX3 containing the 9 amino acid Ca2+ domain (Cad) from CAX1 (CAX3-9) displayed altered stress sensitivities similar to CAX1-expressing plants, whereas CAX3-9-expressing plants did not have any altered stress sensitivities. A single leucine-to-isoleucine change at position 87 (CAX3-I) within the Cad of CAX3 allows this protein to weakly transport Ca2+ in yeast (less than 10% of CAX1). Site-directed mutagenesis of the leucine in the CAX3 Cad demonstrated that no amino acid change tested could confer more activity than CAX3-I. Transport studies in yeast demonstrated that the first three amino acids of the CAX1 Cad could confer twice the Ca2+ transport capability compared to CAX3-I. The entire Cad of CAX3 (87–95) inserted into CAX1 abolishes CAX1-mediated Ca2+ transport. However, single, double, or triple amino acid replacements within the native CAX1 Cad did not block CAX1 mediated Ca2+ transport. Together these findings suggest that other domains within CAX1 and CAX3 influence Ca2+ transport. This study has implications for the ability to engineer CAX-mediated transport in plants by manipulating Cad residues. [ABSTRACT FROM AUTHOR]

Xanthomonas campestris pv. campestris induces two types of symptoms, namely, black rot and blight. Black rot symptoms are V-shaped lesions and black veins on the leaf, and blight symptoms are sudden collapse of interveinal tissues following the lack of veinal necrosis at early stages of infection. These two symptoms can occur simultaneously. However, the tendency to induce either symptom type is strain-dependent. Six strains were evaluated for their rate and pattern of spread in misted seedbeds by using strain-specific monoclonal antibodies and miniplate enrichment/ELISA. Data on pathogen incidence was defined as the presence of the pathogen in or on plants rather than visual symptoms. The results indicated that blight-inducing strains spread to more seedlings than black rot-inducing strains. The high incidences of blight-inducing strains in experimental plots were associated with non-randomness of spatial pattern of pathogen spread, indicating that high incidence is primarily due to the spread from adjacent plants by leaf contact and water splash. Most ELISA-positive seedlings were symptomless, indicating that the sensitivity of the system used in this study was adequate for detection of latent or epiphytic spread. [ABSTRACT FROM AUTHOR]