Expression of the Theobroma cacao Bax-inhibitor-1 gene in tomato reduces infection by the hemibiotrophic pathogen Moniliophthora perniciosa.

Programmed cell death (PCD) plays a key role in plant responses to pathogens, determining the success of infection depending on the pathogen lifestyle and on which participant of the interaction triggers cell death. The hemibiotrophic basidiomycete Moniliophthora perniciosa is the causal agent of witches' broom disease of Theobroma cacao L. (cacao), a serious constraint for production in South America and the Caribbean. It has been hypothesized that M. perniciosa pathogenesis involves PCD, initially as a plant defence mechanism, which is diverted by the fungus to induce necrosis during the dikaryotic phase of the mycelia. Here, we evaluated whether the expression of a cacao anti-apoptotic gene would affect the incidence and severity of M. perniciosa infection using the 'Micro-Tom' (MT) tomato as a model. The cacao Bax-inhibitor-1 (TcBI-1) gene, encoding a putative basal attenuator of PCD, was constitutively expressed in MT to evaluate function. Transformants expressing TcBI-1, when treated with tunicamycin, an inducer of endoplasmic reticulum stress, showed a decrease in cell peroxidation. When the same transformants were inoculated with the necrotrophic fungal pathogens Sclerotinia sclerotiorum, Sclerotium rolfsii and Botrytis cinerea, a significant reduction in infection severity was observed, confirming TcBI-1 function. After inoculation with M. perniciosa, TcBI-1 transformant lines showed a significant reduction in disease incidence compared with MT. The overexpression of TcBI-1 appears to affect the ability of germinating spores to penetrate susceptible tissues, restoring part of the non-host resistance in MT against the S-biotype of M. perniciosa.

Down-regulation of tomato PHYTOL KINASE strongly impairs tocopherol biosynthesis and affects prenyllipid metabolism in an organ-specific manner.

Tocopherol, a compound with vitamin E (VTE) activity, is a conserved constituent of the plastidial antioxidant network in photosynthetic organisms. The synthesis of tocopherol involves the condensation of an aromatic head group with an isoprenoid prenyl side chain. The latter, phytyl diphosphate, can be derived from chlorophyll phytol tail recycling, which depends on phytol kinase (VTE5) activity. How plants co-ordinate isoprenoid precursor distribution for supplying biosynthesis of tocopherol and other prenyllipids in different organs is poorly understood. Here, Solanum lycopersicum plants impaired in the expression of two VTE5-like genes identified by phylogenetic analyses, named SlVTE5 and SlFOLK, were characterized. Our data show that while SlFOLK does not affect tocopherol content, the production of this metabolite is >80% dependent on SlVTE5 in tomato, in both leaves and fruits. VTE5 deficiency greatly impacted lipid metabolism, including prenylquinones, carotenoids, and fatty acid phytyl esters. However, the prenyllipid profile greatly differed between source and sink organs, revealing organ-specific metabolic adjustments in tomato. Additionally, VTE5-deficient plants displayed starch accumulation and lower CO2 assimilation in leaves associated with mild yield penalty. Taken together, our results provide valuable insights into the distinct regulation of isoprenoid metabolism in leaves and fruits and also expose the interaction between lipid and carbon metabolism, which results in carbohydrate export blockage in the VTE5-deficient plants, affecting tomato fruit quality.

microRNA156-targeted SPL/SBP box transcription factors regulate tomato ovary and fruit development.

Fruit ripening in tomato (Solanum lycopersicum L.) is well understood at the molecular level. However, information regarding genetic pathways associated with tomato ovary and early fruit development is still lacking. Here, we investigate the possible role(s) of the microRNA156/SQUAMOSA promoter-binding protein-like (SPL or SBP box) module (miR156 node) in tomato ovary development. miR156-targeted S. lycopersicum SBP genes were dynamically expressed in developing flowers and ovaries, and miR156 was mainly expressed in meristematic tissues of the ovary, including placenta and ovules. Transgenic tomato cv. Micro-Tom plants over-expressing the AtMIR156b precursor exhibited abnormal flower and fruit morphology, with fruits characterized by growth of extra carpels and ectopic structures. Scanning electron microscopy and histological analyses showed the presence of meristem-like structures inside the ovaries, which are probably responsible for the ectopic organs. Interestingly, expression of genes associated with meristem maintenance and formation of new organs, such as LeT6/TKN2 (a KNOX-like class I gene) and GOBLET (a NAM/CUC-like gene), was induced in developing ovaries of transgenic plants as well as in the ovaries of the natural mutant Mouse ear (Me), which also displays fruits with extra carpels. Conversely, expression of the MADS box genes MACROCALYX (MC) and FUL1/TDR4, and the LEAFY ortholog FALSIFLORA, was repressed in the developing ovaries of miR156 over-expressors, suggesting similarities with Arabidopsis at this point of the miR156/SPL pathway but with distinct functional consequences in reproductive development. Altogether, these observations suggest that the miR156 node is involved in maintenance of the meristematic state of ovary tissues, thereby controlling initial steps of fleshy fruit development and determinacy.