Functional Characterization and in Silico Analysis of Phytoene Synthase Family Genes Responsible for Carotenoid Biosynthesis in Watermelon (Citrullus lanatus L.)

Abstract

Carotenoids are the main pigments in watermelon (Citrullus lanatus L.) fruit and contribute to its aesthetic and nutritional value. Phytoene synthase (PSY) is reported to be the first rate-limiting enzyme in carotenogenesis and controls the carotenoid flux. This study aimed to identify PSY genes responsible for carotenoid biosynthesis in the red-fleshed watermelon cultivar LSW-177. The PSY gene members ClPSY1, ClPSY2 and ClPSY3 were characterized and their catalytic activities were displayed in the heterologous complementation assay. The transcript levels of ClPSY genes at the different developmental stages of LSW-177 fruit and the promoter sequence of ClPSY1 were also analyzed. Transcription factors involved in regulating the ClPSY1 expression were scanned with previous RNA-seq data of the different stages during fruit ripening. Results showed that the PSY proteins from watermelon LSW-177 contained the conserved PSY domains and exhibited the ability to condense GGPP into phytoene in E. coli. ClPSY1 is the dominant carotenogenic gene during fruit ripening; and can be induced by light and hormones. Furthermore, Cla013914 and Cla007950 that, respectively encode the transcription factors WD40-like protein and bZIP, likely upregulate ClPSY1 during fruit ripening. In conclusion, ClPSY1 play a dominant role in carotenoid biosynthesis during watermelon fruit ripening and is regulated by complex light and hormone-responsive networks.

Challenges and Opportunities of Light-Emitting Diode (LED) as Key to Modulate Antioxidant Compounds in Plants. A Review

“…Light quality and intensity, as well as temperature, and storage conditions highly influence the photosynthetic process through the content of photosynthetic pigments, [ 126 , 127 , 128 ]. As reported for the phenolic compounds, also the chlorophyll and carotenoid biosynthesis can be regulated by light-responsive genes [ 129 , 130 , 131 ].…”

Comparative transcriptomic and plastid development analysis sheds light on the differential carotenoid accumulation in kiwifruit flesh

“…Directing the flux (GGPP) towards carotenogenesis is the key known function of PSY gene ( Camagna et al., 2019 ). Phytoene synthase ( PSY ) regulates the rate-limiting step of carotenogenesis in most of the plant species and its function in increasing carotenoid levels in tomato ( Giorio et al., 2008 ; Efremov et al., 2020 ), watermelon ( Wu et al., 2020 ), loquat ( Fu et al., 2014 ), maize ( Li et al., 2008 ), banana ( Dhandapani et al., 2017 ), apple ( Ampomah-Dwamena et al., 2015 ) has been extensively studied. Overexpression of PSY gene leads to an increase in carotenoid concentration in several plant species whereas low expression levels result in a decrease in carotenoid content ( Efremov et al., 2020 ).…”

“…The expression levels of regulatory enzymes such as ORANGE (OR), OR-LIKE (OR-L), STAY-GREEN (SGR), and STAY-GREEN LIKE (SGR-L) were investigated in the transcriptomic data (Figure 6; Supplementary File 2, Table 1). The OR gene regulates PSY posttranscriptionally and post-translationally, thereby stabilizing PSY protein and increasing carotenoid concentration (Park et al, 2016;Sun et al, 2020). The expression of three OR genes was detected in the transcriptome with OR2 exhibiting the highest transcript accumulation in A. valvata compared to A. arguta.…”

“…It has also been associated with expanding sink capacity (Sun et al, 2018). The naturally occurring melon OR-His (with a histidine instead of arginine in the active binding site of the protein) regulates chromoplast size and number by binding to a plastid division factor (ARC3), thus interfering its interaction with another plastid division factor (PARC6), to impair binary fission of chromoplast (Sun et al, 2020). High expression levels of OR2 gene in A. valvata may be responsible for the enlarged crystalline chromoplasts observed during fruit maturation (Figure 6; Supplementary File 2, Table 1).…”

“…The OR protein prevents PSY protein aggregation via its holdase chaperone activity thereby stabilizing PSY protein (Park et al, 2016). A change of an Arginine to a Histidine (Arg 108 ➔ His) of the OR protein (a naturally occurring mutation) results in an increase in carotenogenesis and chromoplast biogenesis in melon (Chayut et al, 2017;Sun et al, 2020).…”