Differential expression of ethylene biosynthetic and receptor genes in pollination-induced senescence of Dendrobium flowers.

Following successful pollination, Dendrobium orchid flowers rapidly undergo senescence. In Dendrobium cv. Khao Chaimongkol, compatible pollination resulted in faster ethylene production and more rapid development of senescence symptoms, such as drooping, epinasty, venation and yellowing, compared with non-pollinated controls or pollination with incompatible pollinia. The DenACS1 and DenACO1 genes in the perianth of florets that had been pollinated with compatible pollinia were expressed more highly than those in non-pollinated open florets. Incompatible pollinia reduced the expression of DenACS1 and DenACO1 genes in the perianth. Transcript levels of the ethylene receptor gene DenERS1 and signaling genes DenEIL1 and DenERF1 showed differential spatial regulation with greater expression in the perianth than in the column plus ovary following compatible pollination. Compatible pollinia increased ethylene production concomitant with premature senescence and the increased expression of the DenACS1 and DenACO1 genes, and suppressed the ethylene receptor gene DenERS1, whereas incompatible pollinia did not stimulate ethylene production nor induce premature senescence but induced higher expression of DenERS1 both in the perianth and in the column plus ovary. These results suggest that the increased ethylene production in open florets pollinated with compatible pollen was partially due to an increase in the expression of DenACS1 and DenACO1 genes. The compatible pollinia induced a negative regulation of DenERS1 which may play an important role in ethylene perception and in modulating ethylene signaling transduction during pollinia-induced flower senescence.

Dendrobium orchids carrying antisense ACC oxidase: small changes in flower morphology and a delay of bud abortion, flower senescence, and abscission of flowers.

Four Dendrobium Sonia 'Earsakul' lines were generated by insertion of one, two or three antisense copies of a Carica papaya gene encoding 1-aminocyclopropane-1-carboxylic acid oxidase (CpACO). Whole vegetative plants of the transgenic lines showed about 50% of the basal ethylene production rate, while the increase in ethylene production in floral buds during opening and open flowers prior to visible senescence was delayed. Detailed analysis of more than 100 parameters in flowering plants showed no effect of antisense ACO on plant morphology and coloration, except for shorter length and width of some of the sepals and petals. In intact plants the water-soaking of floral buds as well as bud abscission were delayed by ACO antisense, as was the time to senescence of open flowers. Pollen viability and pollen tube growth were not affected in the transgenic lines. In cut inflorescences placed in water, bud yellowing, bud water soaking, and bud abscission were considerably delayed by the antisense construct, while the life span of open flowers were increased and abscission of open flowers were delayed. It is concluded that the reduction of ACO activity affected the shape of some petals/sepals and delayed the abortion in floral buds, and the senescence and abscission of open flowers.

The effect of 1-methylcyclopropene (1-MCP) on expression of ethylene receptor genes in durian pulp during ripening.

Rapid fruit ripening is a significant problem that limits the shelf life of durian, with ethylene having a major impact on the regulation of this event. Durian treated with ethephon ripened 3 d after treatment with increased pulp total soluble solids, ethylene production of the whole fruit and decreased pulp firmness compared to the control fruit. 1-MCP treatment delayed ripening by up to 9 d with inhibited accumulation of total soluble solids, color change, softening and ethylene production. Genes related to ethylene perception (DzETR1 and DzETR2) and the signaling pathway (DzCTR1, DzEIL1 and DzEIL2) in the pulp were investigated during this process, using qPCR to quantify changes in gene transcription. All candidate genes were significantly up-regulated in ripening durian pulp. Ethephon treatment increased the expression of DzETR1 and DzETR2 genes, while expression of DzCTR1, DzEIL1 and DzEIL2 were slightly affected. 1-MCP treatment significantly inhibited the expression of the DzETR2 and DzEIL1 genes. The promoters of DzETR2 genes were isolated and their activation by fruit transcription factors studied using transient expression in tobacco leaves. It was found that members of the kiwifruit and apple EIL1, EIL2 and EIL3 genes strongly activated the DzETR2 promoter. These results suggest that ethylene-induced ripening of durian is via the regulation of DzETR2 by EIL transcription factors.

Ethylene and pollination decrease transcript abundance of an ethylene receptor gene in Dendrobium petals.

We studied the expression of a gene encoding an ethylene receptor, called Ethylene Response Sensor 1 (Den-ERS1), in the petals of Dendrobium orchid flowers. Transcripts accumulated during the young floral bud stage and declined by the time the flowers had been open for several days. Pollination or exposure to exogenous ethylene resulted in earlier flower senescence, an increase in ethylene production and a lower Den-ERS1 transcript abundance. Treatment with 1-methylcyclopropene (1-MCP), an inhibitor of the ethylene receptor, decreased ethylene production and resulted in high transcript abundance. The literature indicates two kinds of ethylene receptor genes with regard to the effects of ethylene. One group shows ethylene-induced down-regulated transcription, while the other has ethylene-induced up-regulation. The present gene is an example of the first group. The 5' flanking region showed binding sites for Myb and myb-like, homeodomain, MADS domain, NAC, TCP, bHLH and EIN3-like transcription factors. The binding site for the EIN3-like factor might explain the ethylene effect on transcription. A few other transcription factors (RAV1 and NAC) seem also related to ethylene effects.

Molecular analysis of Fiji disease virus segments 2, 4 and 7 completes the genome sequence.

The complete nucleotide sequences of Fiji disease virus (FDV) genome segments S2, S4 and S7 were determined. This now completes the sequencing of all ten dsRNA genome segments of the Fijivirus type member, FDV, which comprises a total of 29339 nt. FDV S2, S4 and S7 comprised 3820, 3568 and 2194 nt, respectively. S2 and S4 each contained a single open reading frame (ORF), which encoded putative proteins of 137 and 133 kDa, respectively, while S7 contained two ORFs, which encoded putative proteins of 42 and 37 kDa. The putative amino acid sequences of FDV S2 and S4 showed most similarity to the gene products of Rice black-streaked dwarf virus (RBSDV) S2 and RBSDV S3, respectively. The putative amino acid sequences of FDV S7 ORF I and II showed most similarity to Maize rough dwarf virus (MRDV) S6 ORF I and RBSDV S7 ORF II, respectively. Phylogenetic analyses showed that FDV was most closely related to the group 2 fijiviruses.