Antisense suppression of a (+)-delta-cadinene synthase gene in cotton prevents the induction of this defense response gene during bacterial blight infection but not its constitutive expression

Monoterpene and sesquiterpene synthases and the origin of terpene skeletal diversity in plants

The multitude of terpene carbon skeletons in plants is formed by enzymes known as terpene synthases. This review covers the monoterpene and sesquiterpene synthases presenting an up-to-date list of enzymes reported and evidence for their ability to form multiple products. The reaction mechanisms of these enzyme classes are described, and information on how terpene synthase proteins mediate catalysis is summarized. Correlations between specific amino acid motifs and terpene synthase function are described, including an analysis of the relationships between active site sequence and cyclization type and a discussion of whether specific protein features might facilitate multiple product formation.

Identification, functional characterization and developmental regulation of sesquiterpene synthases from sunflower capitate glandular trichomes

BACKGROUND

Sesquiterpene lactones are characteristic metabolites of Asteraceae (or Compositae) which often display potent bioactivities and are sequestered in specialized organs such as laticifers, resin ducts, and trichomes. For characterization of sunflower sesquiterpene synthases we employed a simple method to isolate pure trichomes from anther appendages which facilitated the identification of these genes and investigation of their enzymatic functions and expression patterns during trichome development.

RESULTS

Glandular trichomes of sunflower (Helianthus annuus L.) were isolated, and their RNA was extracted to investigate the initial steps of sesquiterpene lactone biosynthesis. Reverse transcription-PCR experiments led to the identification of three sesquiterpene synthases. By combination of in vitro and in vivo characterization of sesquiterpene synthase gene products in Escherichia coli and Saccharomyces cerevisiae, respectively, two enzymes were identified as germacrene A synthases, the key enzymes of sesquiterpene lactone biosynthesis. Due to the very low in vitro activity, the third enzyme was expressed in vivo in yeast as a thioredoxin-fusion protein for functional characterization. In in vivo assays, it was identified as a multiproduct enzyme with the volatile sesquiterpene hydrocarbon delta-cadinene as one of the two main products with alpha-muuorlene, beta-caryophyllene, alpha-humulene and alpha-copaene as minor products. The second main compound remained unidentified. For expression studies, glandular trichomes from the anther appendages of sunflower florets were isolated in particular developmental stages from the pre- to the post-secretory phase. All three sesquiterpene synthases were solely upregulated during the biosynthetically active stages of the trichomes. Expression in different aerial plant parts coincided with occurrence and maturity of trichomes. Young roots with root hairs showed expression of the sesquiterpene synthase genes as well.

CONCLUSION

This study functionally identified sesquiterpene synthase genes predominantly expressed in sunflower trichomes. Evidence for the transcriptional regulation of sesquiterpene synthase genes in trichome cells suggest a potential use for these specialized cells for the identification of further genes involved in the biosynthesis, transport, and regulation of sesquiterpene lactones.

Molecular characterization and temporal expression analyses indicate that the MIC (Meloidogyne Induced Cotton) gene family represents a novel group of root-specific defense-related genes in upland cotton (Gossypium hirsutum L.)

The molecular events underlying the resistance of Upland cotton (Gossypium hirsutum L.) to the root-knot nematode (RKN) are largely unknown. In this report, we further characterize the previously identified MIC3 gene including the identification of 14 related MIC cDNAs in nematode-infected roots of allotetraploid cotton that show >85% identity with MIC3. A time-course analysis of RKN infection in resistant and susceptible cotton lines showed that maximum MIC transcript accumulation occurred immediately prior to the phenotypic manifestation of resistance. MIC expression was not induced by mechanical wounding or by virulent reniform nematode infection. MIC expression was undetectable in cotton leaves undergoing a hypersensitive response to Xanthomonas campestris. A time-course analysis of defense gene expression (PR10, ERF5, CDNS, LOX1, POD4, POD8) in resistant and susceptible cotton roots showed that RKN infection specifically elicits the induction of MIC in resistant roots and not other common defense-signaling pathways. These results suggest that cotton resistance to RKN involves novel defense-signaling pathways and further supports the idea that the MIC genes are intimately involved in this resistance response and represent a group of root-specific defense-related genes in cotton.

The in vitro effect of gossypol and its interaction with salts on conidial germination and viability of Fusarium oxysporum sp. vasinfectum isolates

AIMS

To assess the effect of different concentrations of gossypol (0, 2, 4, 10 and 20 mg l(-1)) in combination with NaCl and Na(2)SO(4) (20 mS cm(-1)) on the conidial germination and viability of Fusarium oxysporum f.sp. vasinfectum (Fov).

METHODS AND RESULTS

A multinomial logistic model was developed to estimate the germination probability of Fov. The inhibitory effect was markedly evident at the two highest concentrations of gossypol; it varied among the isolates tested and with time, and it was attenuated by the presence of sodium salts. The inhibition was temporary as the germination probability increased after 8 h. Fluorescent staining revealed that gossypol either killed the conidia or retarded the elongation of the germ tubes.

CONCLUSION

Fov showed the ability to overcome gossypol inhibition over time, and the inhibitory effect is reduced under saline conditions. Differential responses among Fov isolates to the presence of gossypol suggest that gossypol tolerance is genetically determined in the pathogen.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study suggests that selecting for high plant gossypol cultivars would have minimal effect on the overall Fov resistance of cotton. A new statistical model was developed to explore the statistical significance of plant-pathogen interactions.

Construction of cDNA library of cotton mutant Xiangmian-18 library during gland forming stage

Gossypol, a secondary metabolite stored in the glands of cotton, protecting cottonseed from consumption of human and monogastric animal. This ability is unique to the tribe Gossypieae. Although the relationship between gossypol and pigment gland has been studied for a long time, the development mechanism of pigment gland has not been investigated at molecular level. Here we described a simple and efficient method for constructing a normalized cDNA library from a cotton mutant, Xiangmian-18, during its pigments gland forming stage. It combined switching mechanism at 5'-end of RNA transcript (SMART) technique and duplex-specific nuclease (DSN) normalization methods. In a model experiment, double-stranded cDNAs were synthesized from mRNAs, processed by normalization and Sfi I restriction endonuclease, and finally the cDNAs were ligated to pDNR-LIB vector. The ligation mixture was transformed into E. coli JM109 by electroporation. Counting the number of colonies, the titer of the original library was 5.86x10(5)cfu/ml in this library. Electrophoresis gel results indicated the fragments ranged from 800bp to 2kb, with the average size of 1400bp. Random picking clones showed that the recombination rate was 94%. The results showed that the cDNA library constructed successfully was a full-length library with high quality, and could be used to screen the genes related to development of pigments gland cottons.

Reduced terpene levels in cottonseed add food to fiber

Using RNA interference (RNAi) technology, the levels of a toxic phytoprotectant have recently been reduced specifically in the seeds of cotton to generate a novel dual-purpose crop. By engineering an endogenous terpene pathway, there is now the exciting potential for an added-value, genetically modified crop with the cash value of the fiber supported by the improved nutritional value and expanded food and feed use for the cottonseed, which is normally a low-value by-product.

Molecular cloning and expression analysis of a RanBP2 zinc finger protein gene in upland cotton (Gossypium hirsutum L.)

Gossypol is an important resistant substance of Gossypium, and its storage organ is pigment gland. Although, the relationship between gossypol and pigment gland has been studied for a long time, the development mechanism of pigment gland has not been revealed up to now in molecular perspective. On the basis of differentially expressed cDNAs fragments at the stage of the cotton gland development using suppression subtractive hybridization (SSH), the complete cDNA sequence of a novel RanBP2 zinc finger protein (ZFP) gene was cloned by rapid amplification of cDNA ends (RACE) from upland cotton (Gossypium hirsutum L.), Xiangmian 18. The cotton RanBP2 ZFP cDNA (GenBank accession number: DQ173926) is 717 base pair (bp) long with an open reading frame encoding 139 amino acids, which encodes a 15.6 kDa protein. The cotton RanBP2 ZFP had three Ran-binding protein (RanBP) two zinc finger motifs and belonged to RanBP2 ZFP family. There is a 292-base non-coding sequence at 3' cDNA end, which includes polyA sequence. Sequence alignment analysis revealed that the cDNA nucleotide and its deduced amino acid sequence are moderately identical to the putative ZFP from other species. The mRNA expressing profiles of the novel ZFP gene was investigated by reverse transcription-polymerase chain reaction (RT-PCR). The result showed that it expressed at different development stages of gland, including the undeveloped stage, developing stage, developed stage and cotyledon stage. However, with the development of pigment gland, the mRNA levels in the gland-developed seed and cotyledon were increased to about 1.5 and 2 folds of that in gland-undeveloped seed, respectively, which suggested that the novel ZFP played a role in the development of the cotton gland.

Engineering cottonseed for use in human nutrition by tissue-specific reduction of toxic gossypol

Global cottonseed production can potentially provide the protein requirements for half a billion people per year; however, it is woefully underutilized because of the presence of toxic gossypol within seed glands. Therefore, elimination of gossypol from cottonseed has been a long-standing goal of geneticists. Attempts were made to meet this objective by developing so-called "glandless cotton" in the 1950s by conventional breeding techniques; however, the glandless varieties were commercially unviable because of the increased susceptibility of the plant to insect pests due to the systemic absence of glands that contain gossypol and other protective terpenoids. Thus, the promise of cottonseed in contributing to the food requirements of the burgeoning world population remained unfulfilled. We have successfully used RNAi to disrupt gossypol biosynthesis in cottonseed tissue by interfering with the expression of the delta-cadinene synthase gene during seed development. We demonstrate that it is possible to significantly reduce cottonseed-gossypol levels in a stable and heritable manner. Results from enzyme activity and molecular analyses on developing transgenic embryos were consistent with the observed phenotype in the mature seeds. Most relevant, the levels of gossypol and related terpenoids in the foliage and floral parts were not diminished, and thus their potential function in plant defense against insects and diseases remained untouched. These results illustrate that a targeted genetic modification, applied to an underutilized agricultural byproduct, provides a mechanism to open up a new source of nutrition for hundreds of millions of people.