Abstract
Using an RNA sequencing (RNA-seq) approach, we analyzed the differentially expressed genes (DEGs) and physiological behaviors of “Manicure Finger” grape plantlets grown in vitro under white, blue, green, and red light. A total of 670, 1601, and 746 DEGs were identified in plants exposed to blue, green, and red light, respectively, compared to the control (white light). By comparing the gene expression patterns with the growth and physiological responses of the grape plantlets, we were able to link the responses of the plants to light of different spectral wavelengths and the expression of particular sets of genes. Exposure to red and green light primarily triggered responses associated with the shade-avoidance syndrome (SAS), such as enhanced elongation of stems, reduced investment in leaf growth, and decreased chlorophyll levels accompanied by the expression of genes encoding histone H3, auxin repressed protein, xyloglucan endotransglycosylase/hydrolase, the ELIP protein, and microtubule proteins. Furthermore, specific light treatments were associated with the expression of a large number of genes, including those involved in the glucan metabolic pathway and the starch and sucrose metabolic pathways; these genes were up/down-regulated in ways that may explain the increase in the starch, sucrose, and total sugar contents in the plants. Moreover, the enhanced root growth and up-regulation of the expression of defense genes accompanied with SAS after exposure to red and green light may be related to the addition of 30 g/L sucrose to the culture medium of plantlets grown in vitro. In contrast, blue light induced the up-regulation of genes related to microtubules, serine carboxypeptidase, chlorophyll synthesis, and sugar degradation and the down-regulation of auxin-repressed protein as well as a large number of resistance-related genes that may promote leaf growth, improve chlorophyll synthesis and chloroplast development, increase the ratio of chlorophyll a (chla)/chlorophyll b (chlb), and decrease the ratio of carbohydrates to proteins in plants. Although exposure to red and green light seems to impose “shade stress” on the plantlets, growth under blue light is comparable to growth observed under white or broad-spectrum light.
Highlights
Light quality plays an important role in plant growth by regulating a plethora of physiological activities
Statistics and Sequencing Quality Assessment of the RNA-Seq Data Based on the above-described growth and physiological features of plants exposed to varying wavelengths of light, we proposed that the expression of genes responsible for the observed changes in grape plantlets may have been differentially altered by the four light treatments
Gene Ontology (GO) Analysis of differentially expressed genes (DEGs) in Plants That Received Different Light Quality Treatments As shown in the results presented in Supplement 2 and Supplement 1: Figure 7, the GO analysis identified 944 (Wvs-B), 2462 (W-vs-G), and 989 (W-vs-R) DEGs that were enriched for the term “cellular component.”
Summary
Light quality plays an important role in plant growth by regulating a plethora of physiological activities. The elongation of the main stem is strongly inhibited when the plant is exposed to red light at irradiances of 70 and 150 μmol m−2 s−1 compared to that when it plant is exposed to white and blue light (Fukuda et al, 2016). Shoot growth in lettuce plants exposed to green light emitted by a light-emitting diode (LED; 510 nm) at 300 μmol m−2 s−1 was increased compared with plants exposed to white fluorescent light (Johkan et al, 2012). The number of leaves/plant and the thickness and area of the leaf blade in A. brasiliana (Macedo et al, 2011) and balloon flower (Liu et al, 2014a) were the greatest in plants grown under blue light than plants grown under other lights, but blue light did not affect total dry matter production in roses (Terfa et al, 2013). Light with a wavelength of 522 nm at 70 μmol m−2 s−1 reduced the fresh and dry masses of leaves and roots of Lactuca sativa and was associated with a reduced intensity of photosynthesis, reduced transpiration rate, and decreased stomatal conductivity compared with both red light (639 nm, 88 and 328 μmol m−2 s−1) and blue light (470 nm, 80 and 328 μmol m−2 s−1) (Golovatskaya and Karnachuk, 2015)
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