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The expression of genes for ethylene biosynthesis, ethylene perception, and cell wall degradation in the fruit cortex and fruit abscission zone (FAZ) was examined in relation to preharvest fruit abscission (PFA) and fruit ripening in ‘Golden Delicious’ and ‘Fuji’ apple (Malus ×domestica Borkh.). PFA, fruit ethylene production, and fruit softening increased rapidly during fruit ripening in ‘Golden Delicious’ apples, whereas no PFA, little fruit ethylene, and gradual fruit softening were recorded in ‘Fuji’ apples. The transcript levels of 1-aminocyclopropane-1-carboxylate (ACC) synthase genes, MdACS1, MdACS3, and MdACS5A, increased rapidly in the fruit cortex of ‘Golden Delicious’ apples during ripening, but not in ‘Fuji’ apples. However, only the level of MdACS5A mRNA was up-regulated in the FAZ of ‘Golden Delicious’ apples. The transcript level of ACC oxidase gene, MdACO1, increased in the fruit cortex for both cultivars but increased only in the FAZ of ‘Golden Delicious’ apples. Expression of the ethylene receptor genes, MdETR1, MdETR2, MdERS1, and MdERS2, increased in the fruit cortex for both cultivars, but only MdETR2 and MdERS2 increased in the FAZ of ‘Golden Delicious’ apples. The transcript levels of MdPG2, a polygalacturonase gene (PG), and MdEG1, a β-1,4-glucanase gene, markedly increased only in the FAZ of ‘Golden Delicious’ apples, whereas only MdPG1 rapidly increased in the fruit cortex of ‘Golden Delicious’ apples. Our results suggested that MdACS5A, MdACO1, MdPG2, and MdEG1 in the FAZ might be related to the difference in PFA between these two cultivars, whereas MdACS1 and MdPG1 were associated with fruit softening.
Effects of naphthaleneacetic acid (NAA) and aminoethoxyvinylglycine (AVG) on young fruit abscission, leaf and fruit ethylene production, and expression of genes related to ethylene biosynthesis and cell wall degradation were examined in ‘Delicious’ apples (Malus ×domestica Borkh.). NAA at 15 mg·L−1 increased fruit abscission and ethylene production of leaves and fruit when applied at the 11-mm stage of fruit development, whereas AVG, an inhibitor of ethylene biosynthesis, at 250 mg·L−1 reduced NAA-induced fruit abscission and ethylene production of leaves and fruit. NAA also increased expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase genes (MdACS5A and MdACS5B), ACC oxidase gene (MdACO1), and ethylene receptor genes (MdETR1a, MdETR1b, MdETR2, MdERS1, and MdERS2) in fruit cortex and fruit abscission zones. However, AVG reduced NAA-induced expression of these genes except for MdERS2 in fruit abscission zones. NAA increased expression of the polygalacturonase gene MdPG2 in fruit abscission zones but not in fruit cortex, whereas AVG reduced NAA-enhanced expression of MdPG2 in fruit abscission zones. The expression of β-1,4-glucanase gene MdCel1 in fruit abscission zones was decreased by NAA but was unaffected by AVG. Our results suggest that ethylene biosynthesis, ethylene perception, and the MdPG2 gene are involved in young fruit abscission caused by NAA.
The effects of 1-methylcyclopropene (1-MCP) and naphthaleneacetic acid (NAA) on fruit set and the expression of genes related to ethylene biosynthesis and perception and cell wall degradation in apple (Malus ×domestica Borkh.) were studied when applied during the normal chemical thinning period. 1-MCP at 209 mg·L−1 had a small negative effect or no effect on the final fruit set, depending on the experiment, but could cause a transient delay of June drop when applied at petal fall or the 10-mm stage in ‘Pioneer McIntosh’ apple. 1-MCP at 160 mg·L−1 had no effect on fruit abscission but induced ethylene production by leaves and fruit of ‘Golden Delicious’ apple. NAA at 6 or 15 mg·L−1 effectively increased fruit abscission in both apple cultivars. NAA enhanced the expression of genes related to ethylene biosynthesis (MdACS5A, MdACS5B, and MdACO1) or perception (MdETR1, MdETR1b, MdETR2, MdERS1, and MdERS2) and cell wall degradation (MdPG2). 1-MCP did not affect the expression of MdACS5A and MdACS5B in the fruit abscission zone (FAZ), although it enhanced the expression of these two genes in the fruit cortex (FC) from 6 hours to 1 day after treatment. The expression of MdACO1 in both tissues was increased by 1-MCP by 3 days post-treatment and thereafter. 1-MCP had only a small influence on the expression of most ethylene receptor genes, with the exception of MdETR1, which was upregulated in the FC to a level similar to that observed for NAA treatment. In response to 1-MCP, in the FAZ, the expression of MdCel1 and MdPG2 was upregulated at the beginning and the end, respectively, of the experiment, but otherwise remained at or below control levels. 1-MCP did not inhibit NAA-induced abscission of young apple fruit, suggesting that abscission does not solely depend on ethylene signal transduction, or that the periods of effectiveness for 1-MCP and ethylene were asynchronous.
Luculia pinceana Hook. (Rubiaceae) is a typical distylous species with dimorphic and long-styled monomorphic populations. Within this study, we developed 13 microsatellite markers from L. pinceana using a modified biotin–streptavidin capture method. Polymorphism of each locus was assessed in 30 individuals from four dimorphic populations and one monomorphic population. The average allele number of these microsatellites was 4.153 per locus ranging from three to seven. The observed and expected heterozygosities were from 0.040 to 0.840 and from 0.571 to 0.769, respectively. Additionally, all 13 identified microsatellite markers were successfully amplified in its related species, L. yunnanensis, 10 of which showed polymorphism. These microsatellite markers could provide a useful tool for further study of the breeding system and the population genetic structure in this species and within other Luculia species.
RAPD marker analyses were completed on parents and progeny of two sweetpotato [Ipomoea batatas (L.) Lam.] crosses to determine the feasibility of genetic linkage map construction. A total of 100 primers was tested and 96 produced amplified genomic DNA fragments. The average number of polymorphisms per primer was 0.69. A total of 134 polyphorphic markers was observed and 74 (60%) segregated 1 band present : 1 band absent as needed for use in genetic linkage mapping of polyploids. The 60% of RAPD markers that segregated 1:1 shows that genetic linkage mapping of the hexaploid sweetpotato by RAPD marker analysis is feasible. Linkage was determined for all markers that segregated 1:1 and five pairs of linked markers were found. These were the first linked molecular markers found in sweetpotato and they show that construction of a genetic linkage map is feasible. A genetic linkage map will be a valuable tool to assist in genetic improvements.
The Himalayan yew, Taxus wallichiana Zucc., is an endangered species with a scatted distribution in the Eastern Himalayas and southwestern China. In the present study, 10 microsatellite markers from the genome of T. wallichiana were developed using the protocol of fast isolation by amplified fragment length polymorphism of sequences containing repeats (FIASCO). Polymorphism of each locus was assessed in 28 samples from four wild populations of the Himalayan yew. The allele number of the microsatellites ranged from two to five with an average of 2.9 per allele. The observed and expected heterozygosity varied from 0.00 to 1.00 and from 0.3818 to 0.7552, respectively. Cross-species amplification in another two yew species showed eight of them holding promise for sister species. Two of the 10 loci (TG126 and TC49) significantly deviated from Hardy-Weinberg expectations. No significant linkage disequilibrium was detected between the comparisons of these loci. These polymorphic microsatellite markers would be useful tools for population genetics studies and assessing genetic variations to establish conservation strategy of this endangered species.