<i>Trichoderma</i> volatiles effecting <i>Arabidopsis</i>:from inhibition to protection against phytopathogenic fungi

Trichoderma species are present in many ecosystems and some strains have the ability to reduce the severity of plant diseases by activating various defence pathways via specific biologically active signaling molecules. Hence we investigated the effects of low molecular weight volatile compounds of Trichoderma asperellum IsmT5 on Arabidopsis thaliana. During co-cultivation of T. asperellum IsmT5 without physical contact to A. thaliana we observed smaller but vital and robust plants. The exposed plants exhibit increased trichome numbers, accumulation of defence-related compounds such as H2O2, anthocyanin, camalexin, and increased expression of defence related genes. We conclude that A. thaliana perceives the Trichoderma volatiles as stress compounds and subsequently initiates multilayered adaptations including activation of signaling cascades to withstand this environmental influence.The prominent headspace volatile of T. asperellum IsmT5 was identified to be 6-pentyl-α-pyrone, which was solely applied to A. thaliana to verify the growth and defence reactions. Most noticeable is that A. thaliana preexposed to 6PP showed significantly reduced symptoms when challenged with Botrytis cinerea and Alternaria brassicicola, indicating that defence-activated plants subsequently became more resistant to pathogen attack. Together, these results support that products that are based on Trichoderma volatiles have the potential being a useful biocontrol agent in agriculture

A transposon-based activation-tagging population in Arabidopsis thaliana (TAMARA) and its application in the identification of dominant developmental and metabolic mutations

AbstractA population of 9471 stable activation-tagged lines was generated by transposable element mediated activation tagging mutagenesis in Arabidopsis (TAMARA) using the maize En/Spm transposon system. Based on DNA gel blot and flanking sequence analysis, this population contains approximately 6000 independent transposon insertions. A greenhouse-based screen identified six dominant or semi-dominant activation tagged mutants with obvious developmental alterations, among these a new pistillata mutant allele. In addition, a subset of 1500 lines was screened by a HPLC based high-throughput method for dominant activation tagged mutants with enhanced contents of phenolic compounds. One dominant activation tagged mutant (hpc1-1D) was isolated showing accumulation of a particular compound due to the upregulation of an R2R3-MYB transcription factor

Update on the role of R2R3-MYBs in the regulation of glucosinolates upon sulfur deficiency

To balance the flux of sulfur (S) into glucosinolates (GSL) and primary metabolites plants exploit various regulatory mechanisms particularly important upon S deficiency (S). The role of MYB34, MYB51 and MYB122 controlling the production of indolic glucosinolates (IGs) and MYB28, MYB29, and MYB76 regulating the biosynthesis of aliphatic glucosinolates (AGs) in Arabidopsis thaliana has not been fully addressed at S conditions yet. We show that the decline in the concentrations of GSL during S depletion does not coincide with the globally decreased transcription of R2R3-MYBs. Whereas the levels of GSL are diminished, the expression of MYB34, MYB51, MYB122, and MYB28 is hardly changed in early phase of S limitation. Furthermore, the mRNA levels of these MYBs start to raise under prolonged S starvation. In parallel, we found that SLIM1 can downregulate the MYBs in vitro as demonstrated in trans-activation assays in cultured Arabidopsis cells with SLIM1 as effector and ProMYB51:uidA as a reporter construct. However, in vivo, only the mRNA of MYB29 and MYB76 correlated with the levels of GSL at S. We propose that the negative effect of SLIM1 on GSL regulatory genes can be overridden by a low GSL signal inducing the transcription of MYBs in a feedback regulatory loop. In accordance with this hypothesis, the expression of MYB34, MYB51, MYB122, and CYP83B1 was further induced in cyp79b2 cyp79b3 mutant exposed to S conditions vs. cyp79b2 cyp79b3 plants grown on control medium. In addition, the possible role of MYBs in the regulation of essential S assimilation enzymes, in the regulation of GSL biosynthesis upon accelerated termination of life cycles, in the mobilization of auxin and lateral root formation at S deficiency is discussed

MYB34, MYB51, and MYB122 Distinctly Regulate Indolic Glucosinolate Biosynthesis in Arabidopsis thaliana

The MYB34, MYB51, and MYB122 transcription factors are known to regulate indolic glucosinolate (IG) biosynthesis in Arabidopsis thaliana. To determine the distinct regulatory potential of MYB34, MYB51, and MYB122, the accumulation of IGs in different parts of plants and upon treatment with plant hormones were analyzed in A. thaliana seedlings. It was shown that MYB34, MYB51, and MYB122 act together to control the biosynthesis of I3M in shoots and roots, with MYB34 controlling biosynthesis of IGs mainly in the roots, MYB51 regulating biosynthesis in shoots, and MYB122 having an accessory role in the biosynthesis of IGs. Analysis of glucosinolate levels in seedlings of myb34, myb51, myb122, myb34 myb51 double, and myb34 myb51 myb122 triple knockout mutants grown in the presence of abscisic acid (ABA), salicylic acid (SA), jasmonate (JA), or ethylene (ET) revealed that: (1) MYB51 is the central regulator of IG synthesis upon SA and ET signaling, (2) MYB34 is the key regulator upon ABA and JA signaling, and (3) MYB122 plays only a minor role in JA/ET-induced glucosinolate biosynthesis. The myb34 myb51 myb122 triple mutant is devoid of IGs, indicating that these three MYB factors are indispensable for IG production under standard growth conditions

Regulation of glucosinolate biosynthesis

Glucosinolates are secondary defense metabolites produced by plants of the order Brassicales, which includes the model species Arabidopsis and many crop species. In the past 13 years, the regulation of glucosinolate synthesis in plants has been intensively studied, with recent research revealing complex molecular mechanisms that connect glucosinolate production with responses to other central pathways. In this review, we discuss how the regulation of glucosinolate biosynthesis is ecologically relevant for plants, how it is controlled by transcription factors, and how this transcriptional machinery interacts with hormonal, environmental, and epigenetic mechanisms. We present the central players in glucosinolate regulation, MYB and basic helix-loop-helix transcription factors, as well as the plant hormone jasmonate, which together with other hormones and environmental signals allow the coordinated and rapid regulation of glucosinolate genes. Furthermore, we highlight the regulatory connections between glucosinolates, auxin, and sulfur metabolism and discuss emerging insights and open questions on the regulation of glucosinolate biosynthesis

Transporters in plant sulfur metabolism

Sulfur is an essential nutrient, necessary for synthesis of many metabolites. The uptake of sulfate, primary and secondary assimilation, the biosynthesis, storage, and final utilization of sulfur (S) containing compounds requires a lot of movement between organs, cells, and organelles. Efficient transport systems of S-containing compounds across the internal barriers or the plasma membrane and organellar membranes are therefore required. Here, we review a current state of knowledge of the transport of a range of S-containing metabolites within and between the cells as well as of their long distance transport. An improved understanding of mechanisms and regulation of transport will facilitate successful engineering of the respective pathways, to improve the plant yield, biotic interaction and nutritional properties of crops

bHLH05 Is an Interaction Partner of MYB51 and a Novel Regulator of Glucosinolate Biosynthesis in Arabidopsis

By means of yeast (Saccharomyces cerevisiae) two-hybrid screening, we identified basic helix-loop-helix transcription factor05 (bHLH05) as an interacting partner of MYB51, the key regulator of indolic glucosinolates (GSLs) in Arabidopsis (Arabidopsis thaliana). Furthermore, we show that bHLH04, bHLH05, and bHLH06/MYC2 also interact with other R2R3-MYBs regulating GSL biosynthesis. Analysis of bhlh loss-of-function mutants revealed that the single bhlh mutants retained GSL levels that were similar to those in wild-type plants, whereas the triple bhlh04/05/06 mutant was depleted in the production of GSL. Unlike bhlh04/06 and bhlh05/06 mutants, the double bhlh04/05 mutant was strongly affected in the production of GSL, pointing to a special role of bHLH04 and bHLH05 in the control of GSL levels in the absence of jasmonic acid. The combination of two specific gain-of-function alleles of MYB and bHLH proteins had an additive effect on GSL levels, as demonstrated by the analysis of the double MYB34-1D bHLH05D94N mutant, which produces 20-fold more indolic GSLs than bHLH05D94N and ecotype Columbia-0 of Arabidopsis. The amino acid substitution D94N in bHLH05D94N negatively affects the interaction with JASMONATE-ZIM DOMAIN protein, thereby resulting in constitutive activation of bHLH05 and mimicking jasmonic acid treatment. Our study revealed the bHLH04, bHLH05, and bHLH06/MYC2 factors as novel regulators of GSL biosynthesis in Arabidopsis