The effect of melatonin treatment on the carotenoid metabolism in broccoli florets during storage was explored. The results indicated that 100 µmol/L of melatonin maintained the sensory quality of broccoli florets, which retarded the increase of the L* value and the decrease of the H value. Melatonin treatment increased the activities of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT) and N-acetylserotonin methyltransferase (ASMT), leading to the enrichment of endogenous melatonin content in broccoli florets. Meanwhile, the treatment inhibited the concentrations of β-carotene, β-cryptoxanthin, zeaxanthin and lutein, which was beneficial in delaying the yellowing of broccoli. In addition, a series of carotenoid biosynthetic genes such as BoPSY, BoPDS, BoZDS, BoLCYβ and BoZEP was also suppressed by melatonin. Further analysis revealed that the lower carotenoid content and the down-regulated BoNCED expression in treated broccoli resulted in less accumulation of abscisic acid precursors, inhibiting abscisic acid production during the yellowing process.
In this study, we report the molecular characterization of clone Eg707 isolated from cell suspension culture of the oil palm. The deduced polypeptide of clone Eg707 is highly similar to an unknown protein from Arabidopsis thaliana. The presence of an Ald-Xan-dh-C2 superfamily domain in the deduced protein sequence suggested that Eg707 protein might be involved in abscisic acid biosynthesis. Eg707 might be present as a single copy gene in the oil palm genome. This gene is highly expressed in tissue cultured materials compared to vegetative and reproductive tissues, suggesting a role of this gene during oil palm somatic embryogenesis or at the early stages of embryo development. Expression analysis of Eg707 by RNA in situ hybridization showed that Eg707 transcripts were present throughout somatic embryo development starting from proembryo formation at the embryogenic callus stages till the maturing embryo stages. Since proembryo formation within the embryogenic callus is one of the first key factors in oil palm somatic embryo development, it is suggested that Eg707 could be used as a reliable molecular marker for detecting early stage of oil palm somatic embryogenesis.
KEY MESSAGE: Potentially embryogenic oil palms can be identified through leaf transcriptomic signatures. Differential expression of genes involved in flowering time, and stress and light responses may associate with somatic embryogenesis potential. Clonal propagation is an attractive approach for the mass propagation of high yielding oil palms. A major issue hampering the effectiveness of oil palm tissue culture is the low somatic embryogenesis rate. Previous studies have identified numerous genes involved in oil palm somatic embryogenesis, but their association with embryogenic potential has not been determined. In this study, differential expression analysis of leaf transcriptomes from embryogenic and non-embryogenic mother palms revealed that transcriptome profiles from non- and poor embryogenic mother palms were more similar than highly embryogenic palms. A total of 171 genes exhibiting differential expression in non- and low embryogenesis groups could also discriminate high from poor embryogenesis groups of another tissue culture agency. Genes related to flowering time or transition such as FTIP, FRIGIDA-LIKE, and NF-YA were up-regulated in embryogenic ortets, suggesting that reproduction timing of the plant may associate with somatic embryogenesis potential. Several light response or photosynthesis-related genes were down-regulated in embryogenic ortets, suggesting a link between photosynthesis activity and embryogenic potential. As expression profiles of the differentially expressed genes are very similar between non- and low embryogenic groups, machine learning approaches with several candidate genes may generate a more sensitive model to better discriminate non-embryogenic from embryogenic ortets.
Genetic improvement is an important approach for crop improvement towards yield stability in stress-prone areas. Functional analysis of candidate stress response genes can provide key information to allow the selection and modification of improved crop varieties. In this study, the constitutive expression of a banana cDNA, MaRHD3 in Arabidopsis improved the ability of transgenic lines to adapt to drought conditions. Transgenic Arabidopsis plants expressing MaRHD3 had roots with enhanced branching and more root hairs when challenged with drought stress. The MaRHD3 plants had higher biomass accumulation, higher relative water content, higher chlorophyll content and an increase in activity of reactive oxygen species (ROS) scavenging enzymes; SOD, CAT, GR, POD and APX with reduced water loss rates compared to control plants. The analysis of oxidative damage indicated lower cell membrane damage in transgenic lines compared to control plants. These findings, together with data from higher expression of ABF-3 and higher ABA content of drought-stressed transgenic MaRHD3 expressing plants, support the involvement of the ABA signal pathway and ROS scavenging enzyme systems in MaRHD3 mediated drought tolerance.
Oil palm is one of the most productive oil-producing crops and can store up to 90% oil in its fruit mesocarp. Oil palm fruit is a sessile drupe consisting of a fleshy mesocarp from which palm oil is extracted. Biochemical changes in the mesocarp cell walls, polyamines, and hormones at different ripening stages of oil palm fruits were studied, and the relationship between the structural and the biochemical metabolism of oil palm fruits during ripening is discussed. Time-course analysis of the changes in expression of polyamines, hormones, and cell-wall-related genes and metabolites provided insights into the complex processes and interactions involved in fruit development. Overall, a strong reduction in auxin-responsive gene expression was observed from 18 to 22 weeks after pollination. High polyamine concentrations coincided with fruit enlargement during lipid accumulation and latter stages of maturation. The trend of abscisic acid (ABA) concentration was concordant with GA₄ but opposite to the GA₃ profile such that as ABA levels increase the resulting elevated ABA/GA₃ ratio clearly coincides with maturation. Polygalacturonase, expansin, and actin gene expressions were also observed to increase during fruit maturation. The identification of the master regulators of these coordinated processes may allow screening for oil palm variants with altered ripening profiles.