Structural and functional features of phytoene synthase isoforms PSY1 and PSY2 in pepper Capsicum annuum L. cultivars

Abstract

The fruits of various pepper cultivars are characterized by a different colour, which is determined by the pigment ratio; carotenoids dominate in ripe fruits, while chlorophylls, in immature fruits. A key regulator of carotenoid biosynthesis is the phytoene synthase encoded by the PSY gene. The Capsicum annuum genome contains two isoforms of this enzyme, localized in leaf (PSY2) and fruit (PSY1) plastids. In this work, the complete PSY1 and PSY2 genes were identified in nine C. annuum cultivars, which differ in ripe fruit colour. PSY1 and PSY2 sequence variability was 2.43 % (69 SNPs) and 1.21 % (36 SNPs). The most variable were PSY1 proteins of the cultivars ‘Maria’ (red-fruited) and ‘Sladkij shokolad’ (red-brown-fruited). All identified PSY1 and PSY2 homologs contained the phytoene synthase domain HH-IPPS and the transit peptide. In the PSY1 and PSY2 HH-IPPS domains, functionally significant sites were determined. For all accessions studied, the active sites (YAKTF and RAYV), aspartate-rich substrate-Mg2+-binding sites (DELVD and DVGED), and other functional residues were shown to be conserved. Transit peptides were more variable, and their similarity in the PSY1 and PSY2 proteins did not exceed 78.68 %. According to the biochemical data obtained, the largest amounts of chlorophylls and carotenoids across the cultivars studied were detected in immature and ripe fruits of the cv. ‘Sladkij shokolad’ and ‘Shokoladnyj’. Also, ripe fruits of the cv. ‘Nesozrevayuschij’ (green-fruited) were marked by significant chlorophyll content, but a minimum of carotenoids. The PSY1 and PSY2 expression patterns were determined in the fruit pericarp at three ripening stages in ‘Zheltyj buket’, ‘Sladkij shokolad’, ‘Karmin’ and ‘Nesozrevayuschij’, which have different ripe fruit colours: yellow, red-brown, dark red and green, respectively. In the leaves of the cultivars studied, PSY1 expression levels varied significantly. All cultivars were characterized by increased PSY1 transcription as the fruit ripened; the maximum transcription level was found in the ripe fruit of ‘Sladkij shokolad’, and the lowest, in ‘Nesozrevayuschij’. PSY2 transcripts were detected not only in the leaves and immature fruits, but also in ripe fruits. Assessment of a possible correlation of PSY1 and PSY2 transcription with carotenoid and chlorophyll content revealed a direct relationship between PSY1 expression level and carotenoid pigmentation during fruit ripening. It has been suggested that the absence of a typical pericarp pigmentation pattern in ‘Nesozrevayuschij’ may be associated with impaired chromoplast formation.

Cloning and Analysis of Expression of Genes Related to Carotenoid Metabolism in Different Fruit Color Mutants of Pepper (Capsicum annuum L.)

“…Its level of expression was highest in cotyledons and lowest in the pericarp. It was detected not only in the leaves and immature fruit but also in mature fruit [ 44 ]. Some studies also found that Psy2 could compensate for the loss of Psy1 in pepper fruit [ 45 ].…”

Characterization of leucine aminopeptidase (LAP) activity in sweet pepper fruits during ripening and its inhibition by nitration and reducing events

“…Likewise, C. annuum has hundreds of varieties and, among other characteristics, two large groups can be made sweet and spicy according to the content of capsaicin (Vázquez-Espinosa et al 2020 ). On the contrary, the ripening process of pepper fruits involves many changes at the phenotypic, transcriptomic, proteomic, and metabolomic levels, and its big genome size, in comparison to other Solanaceae, makes its analysis complex (Dyachenko et al 2020 ; Razo-Mendivil et al 2021 ; Esposito et al 2022 ; Kovács et al 2022 ; Del Giúdice et al 2023 ). Recently, “omic” approaches have been carried out to study specific aspects of the ripening process (Chiaiese et al 2019 ; Dubey et al 2019 ; Zuo et al 2019 ; Lopez-Ortiz et al 2021 ; Rödiger et al 2021 ; Momo et al 2022 ; Villa-Rivera et al 2022 ; Song et al 2022 ; Liu et al 2023 ; Wang et al 2024 ) which are dependent on the variety, environmental growth conditions, fruit position, and ripening stage (Ribes-Moya et al 2020 ; Jang et al 2022 ; Lahbib et al 2023 ; Guijarro-Real et al 2023 ; Islam et al 2023 ).…”

Comparative transcriptome analysis reveals that chlorophyll metabolism contributes to leaf color changes in wucai (Brassica campestris L.) in response to cold

“…Car coordinates with Chl in chloroplasts and is an important component in photosynthetic organs and photoprotective systems [ 31 ]. Car accumulates in plastids and forms different colors in plants [ 32 – 35 ], such as orange, yellow or red [ 36 ]. The Chl and Car contents and the total Chl/Car ratio of LT leaves were lower than NT at the same period (Fig.…”

“…PSY and PDS are key enzymes in Car biosynthesis [ 37 , 38 ]. The mutation of PSY and PDS can cause the decrease of carotenoid content [ 32 , 39 , 40 ]. In our study, the expression levels of PSY and PDS were significantly decreased under LT, which can explain the yellow leaves under LT.…”