Identification of an Abscisic Acid Gene Cluster in the Grey Mold Botrytis cinerea

Like several other phytopathogenic fungi, the ascomycete Botrytis cinerea is known to produce the plant hormone abscisic acid (ABA) in axenic culture. Recently, bcaba1, the first fungal gene involved in ABA biosynthesis, was identified. Neighborhood analysis of bcaba1 revealed three further candidate genes of this pathway: a putative P450 monooxygenase-encoding gene (bcaba2), an open reading frame without significant similarities (bcaba3), and a gene probably coding for a short-chain dehydrogenase/reductase (bcaba4). Targeted inactivation of the genes proved the involvement of BcABA2 and BcABA3 in ABA biosynthesis and suggested a contribution of BcABA4. The close linkage of at least three ABA biosynthetic genes is strong evidence for the presence of an abscisic acid gene cluster in B. cinerea.     

Identification of an abscisic acid gene cluster in the grey mold Botrytis cinerea

Like several other phytopathogenic fungi, the ascomycete Botrytis cinerea is known to produce the plant hormone abscisic acid (ABA) in axenic culture. Recently, bcaba1, the first fungal gene involved in ABA biosynthesis, was identified. Neighborhood analysis of bcaba1 revealed three further candidate genes of this pathway: a putative P450 monooxygenase-encoding gene (bcaba2), an open reading frame without significant similarities (bcaba3), and a gene probably coding for a short-chain dehydrogenase/reductase (bcaba4). Targeted inactivation of the genes proved the involvement of BcABA2 and BcABA3 in ABA biosynthesis and suggested a contribution of BcABA4. The close linkage of at least three ABA biosynthetic genes is strong evidence for the presence of an abscisic acid gene cluster in B. cinerea.     

Biosynthesis of abscisic acid in fungi: identification of a sesquiterpene cyclase as the key enzyme in Botrytis cinerea

While abscisic acid (ABA) is known as a hormone produced by plants through the carotenoid pathway, a small number of phytopathogenic fungi are also able to produce this sesquiterpene but they use a distinct pathway that starts with the cyclization of farnesyl diphosphate (FPP) into 2Z,4E‐α‐ionylideneethane which is then subjected to several oxidation steps. To identify the sesquiterpene cyclase (STC) responsible for the biosynthesis of ABA in fungi, we conducted a genomic approach in Botrytis cinerea. The genome of the ABA‐overproducing strain ATCC58025 was fully sequenced and five STC‐coding genes were identified. Among them, Bcstc5 exhibits an expression profile concomitant with ABA production. Gene inactivation, complementation and chemical analysis demonstrated that BcStc5/BcAba5 is the key enzyme responsible for the key step of ABA biosynthesis in fungi. Unlike what is observed for most of the fungal secondary metabolism genes, the key enzyme‐coding gene Bcstc5/Bcaba5 is not clustered with the other biosynthetic genes, i.e., Bcaba1 to Bcaba4 that are responsible for the oxidative transformation of 2Z,4E‐α‐ionylideneethane. Finally, our study revealed that the presence of the Bcaba genes among Botrytis species is rare and that the majority of them do not possess the ability to produce ABA.     

Abscisic acid (ABA) treatment increases artemisinin content in <Emphasis Type="Italic">Artemisia annua</Emphasis> by enhancing the expression of genes in artemisinin biosynthetic pathway

Artemisinin, a sesquiterpene lactone endoperoxide derived from Artemisia annua L., is the most effective antimalarial drug. In an effort to increase the artemisinin production, abscisic acid (ABA) with different concentrations (1, 10 and 100 μM) was tested by treating A. annua plants. As a result, the artemisinin content in ABA-treated plants was significantly increased. Especially, artemisinin content in plants treated by 10 μM ABA was 65% higher than that in the control plants, up to an average of 1.84% dry weight. Gene expression analysis showed that in both the ABA-treated plants and cell suspension cultures, HMGR, FPS, CYP71AV1 and CPR, the important genes in the artemisinin biosynthetic pathway, were significantly induced. While only a slight increase of ADS expression was observed in ABA-treated plants, no expression of ADS was detected in cell suspension cultures. This study suggests that there is probably a crosstalk between the ABA signaling pathway and artemisinin biosynthetic pathway and that CYP71AV1, which was induced most significantly, may play a key regulatory role in the artemisinin biosynthetic pathway.     

Sequence and characterization of 6 Lea proteins and their genes from cotton

Lea genes code for mRNAs and proteins that are late embryogenesis abundant in higher plant seed embryos. They appear to be ubiquitous in higher plants and may be induced to high levels of expression in other tissues and at other times of ontogeny by ABA and/or desiccation. Presented here are the genomic and cDNA sequences for 6 of these genes from cotton seed embryos and the derived amino acid sequences of the corresponding proteins.The Lea genes contain the standard sequence features of eucaryotic genes (TATA box and poly (A) addition sequences) and have 1 or more introns. Sequences differences between cDNA and genomic DNA confirm the existence of small multigene families for several Lea genes. The amino acid composition and sequence for the Lea proteins are unusual. Five are extremely hydrophilic, four contain no cys or trp and 4 have sequence domains that suggest amphiphilic helical structures. Hypothetical functions in desiccation survival, based on amino acid sequence, are discussed.     

Involvement of abscisic acid in ozone-induced puerarin production of Pueraria thomsnii Benth. suspension cell cultures

Exposure to ozone induced a rapid increase in the levels of the sesquiterpene phytohormone abscisic acid (ABA) and the isoflavone puerarin in suspension cell cultures of Pueraria thomsnii Benth. The observed increases in ABA and puerarin were dependent on the concentration of ozone applied to P. thomsnii cell cultures. In order to examine the role of ABA in ozone-induced puerarin production, cell suspensions were pretreated with the ABA biosynthetic inhibitor fluridone. Following ozone exposure, fluridone treatment suppressed ABA accumulation suggesting ABA was normally synthesized de novo through the carotenoid pathway. Fluridone also blocked ozone-induced puerarin production, which could be reversed through application of exogenous ABA. However, in the absence of ozone, ABA itself had no effect on puerarin accumulation in the suspension cells. Taken together, the data indicate that ozone is an efficient elicitor of puerarin production and may be particularly applicable for improving puerarin production in plant cell cultures. Furthermore, we demonstrate that ABA is one factor associated with ozone-induced puerarin production in P. thomsnii cell cultures.     

Origin and evolution of genes related to ABA metabolism and its signaling pathways

Since plants cannot move to avoid stress, they have sophisticated acclimation mechanisms against a variety of abiotic stresses. The phytohormone abscisic acid (ABA) plays essential roles in abiotic stress tolerances in land plants. Therefore, it is interesting to address the evolutionary origins of ABA metabolism and its signaling pathways in land plants. Here, we focused on 48 ABA-related Arabidopsis thaliana genes with 11 protein functions, and generated 11 orthologous clusters of ABA-related genes from A. thaliana, Arabidopsis lyrata, Populus trichocarpa, Oryza sativa, Selaginella moellendorffii, and Physcomitrella patens. Phylogenetic analyses suggested that the common ancestor of these six species possessed most of the key protein functions of ABA-related genes. In two species (A. thaliana and O. sativa), duplicate genes related to ABA signaling pathways contribute to the expression variation in different organs or stress responses. In particular, there is significant expansion of gene families related to ABA in evolutionary periods associated with morphological divergence. Taken together, these results suggest that expansion of the gene families related to ABA signaling pathways may have contributed to the sophisticated stress tolerance mechanisms of higher land plants.     

Potential Pathogenicity of Candida maltosa IAM 12248

The stereochemistry of (+)-(2Z,4E)-trans-1′,4′-dihydroxy-γ-ionylideneacetic acid, a major metabolite from Cercospora cruenta, a fungus found to produce (+)-abscisic acid, was reexamined as to its ¹H?¹H-Cosy and Noesy 2D-NMR spectra, and it was proved to have a chair conformation with an axial pentadienoate moiety. Further, the metabolism of (+)-[14C]-1′,4′-dihydroxy-γ-ionylideneacetic acid in tomato plants suggested the possibility of it being a biosynthetic intermediate of ABA in plants.     

Pepper protein phosphatase type 2C,CaADIP1 and its interacting partner CaRLP1 antagonistically regulate ABA signalling and drought response

Abscisic acid (ABA) is a key phytohormone that regulates plant growth and developmental processes, including seed germination and stomatal closing. Here, we report the identification and functional characterization of a novel type 2C protein phosphatase, CaADIP1 (Capsicum annuum A BA and D rought‐I nduced P rotein phosphatase 1). The expression of CaADIP1 was induced in pepper leaves by ABA, drought and NaCl treatments. Arabidopsis plants overexpressing CaADIP1 (CaADIP1‐OX) exhibited an ABA‐hyposensitive and drought‐susceptible phenotype. We used a yeast two‐hybrid screening assay to identify CaRLP1 (Capsicum annuum R CAR‐L ike P rotein 1), which interacts with CaADIP1 in the cytoplasm and nucleus. In contrast to CaADIP1‐OX plants, CaRLP1‐OX plants displayed an ABA‐hypersensitive and drought‐tolerant phenotype, which was characterized by low levels of transpirational water loss and increased expression of stress‐responsive genes relative to those of wild‐type plants. In CaADIP1‐OX/CaRLP1‐OX double transgenic plants, ectopic expression of the CaRLP1 gene led to strong suppression of CaADIP1‐induced ABA hyposensitivity during the germinative and post‐germinative stages, indicating that CaADIP1 and CaRLP1 act in the same signalling pathway and CaADIP1 functions downstream of CaRLP1. Our results indicate that CaADIP1 and its interacting partner CaRLP1 antagonistically regulate the ABA‐dependent defense signalling response to drought stress.