Biochemical and physiological mode of action of tiafenacil, a new protoporphyrinogen IX oxidase-inhibiting herbicide.

We conducted biochemical and physiological experiments to investigate the mode of action of tiafenacil (Terrad'or™), a new protoporphyrinogen IX oxidase (PPO)-inhibiting pyrimidinedione herbicide. Analysis of the half-maximal inhibitory concentration (IC50) against recombinant PPO enzymes from various plant species, including amaranth (Amaranthus tuberculatus), soybean (Glycine max), arabidopsis (Arabidopsis thaliana), and rapeseed (Brassica napus), showed that tiafenacil had an IC50 of 22 to 28 nM, similar to the pyrimidinedione herbicides butafenacil and saflufenacil and the N-phenylphthalimide herbicide flumioxazin. By contrast, tiafenacil exhibited 3- to 134-fold lower IC50 values than the diphenyl ether herbicides fomesafen, oxyfluorfen, and acifluorfen. Tiafenacil is non-selective and is herbicidal to both dicots and monocots, such as the weeds velvetleaf (Abutilon theophrasti), amaranth, and barnyardgrass (Echinochloa crus-galli) as well as the crops soybean, rapeseed, rice (Oryza sativa), and maize (Zea mays) at concentrations ranging from 1 to 50 µM. Treatment of plant tissue with tiafenacil in darkness resulted in the accumulation of protoporphyrin IX. Subsequent exposure to light increased the content of malondialdehyde and significantly decreased the Fv/Fm values of chlorophyll fluorescence. The results suggest that tiafenacil is a new PPO-inhibiting pyrimidinedione herbicide.

Isolation and promoter analysis of anther-specific genes encoding putative arabinogalactan proteins in Malus x domestica.

In this study, we searched for anther-specific genes involved in male gametophyte development in apple (Malus x domestica Borkh. cv. Fuji) by differential display-PCR. Three full-length cDNAs were isolated, and the corresponding genomic sequences were determined by genome walking. The identified genes showed intronless 228- to 264-bp open reading frames and shared 82-90% nucleotide sequence. Sequence analysis identified that they encoded a putative arabinogalactan protein (AGP) and were designated MdAGP1, MdAGP2, and MdAGP3, respectively. RT (reverse transcriptase)-PCR revealed that the MdAGP genes were selectively expressed in the stamen. Promoter analysis confirmed that the MdAGP3 promoter was capable of directing anther- or pollen-specific expression of the GUS reporter in tobacco and apple. Furthermore, expression of ribosome-inactivating protein under the control of the MdAGP3 promoter induced complete sporophytic male sterility as we had expected.

Microarray analysis of apple gene expression engaged in early fruit development.

To evaluate gene expressions mostly engaged in early development of apple fruit, we performed the identification of transcripts differentially expressed in young fruit by using microarrays spotted with 6,253 cDNAs collected from young and mature apple fruits of the cultivar Fuji (Malus domestica Borkh. cv. Fuji). A total of 3,484 cDNAs out of 6,253 were selected after quality control of microarray spots and analyzed for differential gene expression patterns between young fruit and other tissues (mature fruit, leaf and flower). Among them, 192 cDNAs displayed a signal value higher than twofold in young fruit compared with other tissues. Blast analysis of the 192 cDNA clones identified 88 non-redundant groups encoding proteins with known function and 50 non-redundant groups with unknown function. The putative protein products were classified into the following categories: photosynthesis (16.7%), protein synthesis (12.3%), cell proliferation and differentiation (10.9%), cell enlargement (5.8%), metabolism (8.0%), stress response (7.2%), others (2.9%), and unknown functions (32.2%). Furthermore, confirming the microarray data by reverse transcription-polymerase chain reaction revealed that the wide range of transcripts differentially expressed in young fruit was expressed in other organs but not in the mature fruit. The data presented suggested that apple fruit development depends on the tight regulation of the expression of a number of genes, which are also expressed in other organs.