Hakeem Shittu

Plant-endophyte interplay protects tomato against a virulent Verticillium.

Endophytes, bacterial, fungal or viral, colonize plants often without causing visible symptoms. More important, they may benefit host plants in many ways, most notably by preventing diseases caused by normally virulent pathogens. Craigella tomatoes (Lycopersicon esculentum Mill.) can be infected with Verticillium dahliae Kleb., either race 1 (Vd1) or a non-host isolate Dvd-E6 resulting in susceptibility or tolerance, respectively. The present study sought to determine whether Dvd-E6 is endophytic and can protect tomato against Vd1. The total amount of Verticillium in stems and roots was determined by quantitative PCR; the relative amounts of Vd1 and Dvd-E6 were assessed by restriction fragment polymorphism. When Dvd-E6 infects before or together with Vd1, Vd1 is excluded almost completely from the root but, when Vd1 infects first, Dvd-E6 can compete on an equal basis. Previous studies suggested that Dvd-E6 suppresses symptom-related genes, raising the possibility that Dvd-E6 simultaneously induces tolerance to Vd1. This does not seem to be entirely the case since the minimal symptoms following Vd1 infection of Dvd-E6 tolerant Craigella result, at least in part, from restricted Vd1 colonization. Furthermore, when Vd1 and Dvd-E6 are cultured on PDA plates alone or together, the growth rates are similar and neither is inhibitory to the other. Dvd-E6 does not outgrow or inhibit Vd1, in vitro. The protective effect apparently requires interplay between Dvd-E6 and the plant. Expression analyses of tomato genes involved in resistance and defence support this interpretation.

Arsenal of elevated defense proteins fails to protect tomato against Verticillium dahliae

Although the hypersensitive reaction in foliar plant diseases has been extensively described, little is clear regarding plant defense strategies in vascular wilt diseases affecting numerous economically important crops and trees. We have examined global genetic responses to Verticillium wilt in tomato (Lycopersicon esculentum Mill.) plants differing in Ve1 resistance alleles. Unexpectedly, mRNA analyses in the susceptible plant (Ve1−) based on the microarrays revealed a very heroic but unsuccessful systemic response involving many known plant defense genes. In contrast, the response is surprisingly low in plants expressing the Ve1+ R-gene and successfully resisting the pathogen. Similarly, whole-cell protein analyses, based on 2D gel electrophoresis and mass spectrometry, demonstrate large systemic increases in a variety of known plant defense proteins in the stems of susceptible plants but only modest changes in the resistant plant. Taken together, the results indicate that the large systemic increases in plant defense proteins do not protect the susceptible plant. Indeed, since a number of the highly elevated proteins are known to participate in the plant hypersensitive response as well as natural senescence, the results suggest that some or all of the disease symptoms, including ultimate plant death, actually may be the result of this exaggerated plant response.

Date Palm Cell and Protoplast Culture

This chapter describes the current status of cell and protoplast cultures in date palm (Phoenix dactylifera L.). Critically important steps toward plant regeneration from recalcitrant date palm protoplasts have been achieved in the recent past. Callus regeneration was achieved in commercial cvs. Deglet Noor, Takerboucht, Barhee and Zaghloul. The use of feeder layer was the main factor for inducing cell divisions as well as subsequent microcallus and callus formation. Presently, a protoplast-to-plant system has been reported for more than 400 species, of which the family Solanaceae is predominantly represented. In crops like potato, tobacco, brassica, citrus and eggplant seed companies are using protoplast fusion based technology to produce new commercial varieties. In the last decade however, little progress has been made regarding protoplast regeneration from the so-called recalcitrant species which includes date palm. There are certain similarities between some protoplast systems and mammalian stem cells. More collaboration between animal and plant scientists is highly encouraged, which would be useful for both parties to help address these challenges.

Endophyte-induced Verticillium protection in tomato is range-restricted

Endophytes, bacterial, fungal or viral, colonize plants often without causing visible symptoms. More important, they may benefit host plants in many ways, most notably by preventing diseases caused by normally virulent pathogens. Previous studies have shown that an isolate of V. dahliae from eggplant, Dvd-E6, can colonize tomato endophytically, producing taller and more robust tomato plants while providing protection against a virulent V. dahliae, race 1 (Vd1) isolate. Expression analyses suggest this requires interplay between Dvd-E6 and the plant that involves resistance and defense genes. To examine the possibility of a broader effect, dual interactions have been further examined with a more distantly related pathogen, Verticillium albo-atrum (Vaa). The results indicate Dvd-E6 colonization selectively modifies the expression of specific tomato genes to be detrimental to Vd1 but not Vaa, providing evidence that Verticillium-induced protection is range-restricted.

Tomato Ve resistance locus; defense or growth

Main conclusionVerticillium colonization does induce a cascade of defense/stress proteins but the Ve1 gene also promotes enhanced root growth, which appears to allow the plant to outgrow the pathogen and avoid symptoms associated with an exaggerated defense response.In tomato, the Ve1 gene provides resistance to the vascular pathogen, Verticillium dahliae, race 1; ve1 plants are susceptible. However, the physiological basis of the resistance is unknown. While developing alternative lines of mutant Ve1 gene transformants to address this question a striking difference was observed in transformation frequency resulting from the inefficient rooting of plantlets from ve1 callus relative to Ve1 callus. Subsequent experiments with resistant and susceptible near-isolines of the cultivar Craigella, as well as Ve1 transformants, showed that in both artificial medium and soil, root growth was significantly enhanced in the resistant cultivar. Parallel studies of Verticillium colonization indicated a significantly lower overall concentration in the resistant plant characteristic of the resistant phenotype, but an almost equal total fungal biomass in both resistant and susceptible roots. Proteomic analyses of the roots of Verticillium-infected plants revealed elevated levels of defense/stress proteins, which correlated with the fungal concentration rather than resistance. Hormone analyses demonstrated a higher cis-ABA level in the resistant isoline consistent with enhanced root growth. Taken together these studies indicate a similar fungal biomass in the roots of both isolines where the Ve1 gene also promotes root production. In the case of the Craigella/Vd1 pathosystem, this appears to allow the host to resist better by outgrowing the pathogen with less wilt rather than reliance only on partial immunity.

Defence cascade in Verticillium-infected grafted tomato

ABSTRACT In tomato the Ve1-gene provides resistance to the vascular pathogen, Verticillium dahliae, race 1; ve1 plants are susceptible. Reciprocal grafts of resistant and susceptible tomato near-isolines were used to examine proteomic changes and, in particular, the effect of the Ve1-gene on the defence/stress protein cascade induced during Verticillium wilt. Based on label-free LC-MS, the results indicate that this defence response is cell-specific, correlates with overall fungal colonization and is mitigated by Ve1 function. The influence of the Ve1-gene in resistant tissues, however, is not actually transferred to susceptible tissues in the grafted plant.