Transcriptome analysis in petals and leaves of chrysanthemums with different chlorophyll levels

Abstract

BackgroundChlorophylls (Chls) are magnesium-containing tetrapyrrole macromolecules responsible for the green color in plants. The Chl metabolic pathway has been intensively studied and nearly all the enzymes involved in the pathway have been identified and characterized. Synthesis and activity of these enzymes are tightly regulated in tissue- and developmental stage–specific manners. Leaves contain substantial amounts of Chls because Chls are indispensable for photosynthesis. In contrast, petals generally contain only trace amounts of Chls, which if present would mask the bright petal color. Limited information is available about the mechanisms that control such tissue-specific accumulation of Chls.ResultsTo identify the regulatory steps that control Chl accumulation, we compared gene expression in petals and leaves of chrysanthemum cultivars with different Chl levels. Microarray and quantitative real-time PCR analyses showed that the expression levels of Chl biosynthesis genes encoding glutamyl-tRNA reductase, Mg-protoporphyrin IX chelatase, Mg-protoporphyrin IX monomethylester cyclase, and protochlorophyllide oxidoreductase were well associated with Chl content: their expression levels were lower in white petals than in green petals, and were highest in leaves. Among Chl catabolic genes, expression of STAY-GREEN, encoding Mg-dechelatase, which is a key enzyme controlling Chl degradation, was considerably higher in white and green petals than in leaves. We searched for transcription factor genes whose expression was well related to Chl level in petals and leaves and found three such genes encoding MYB113, CONSTANS-like 16, and DREB and EAR motif protein.ConclusionsFrom our transcriptome analysis, we assume that a low rate of Chl biosynthesis and a high rate of Chl degradation lead to the absence of Chls in white chrysanthemum petals. We identified several candidate transcription factors that might affect Chl accumulation in chrysanthemum petals. Functional analysis of these transcription factors will provide a basis for future molecular studies of tissue-specific Chl accumulation.Electronic supplementary materialThe online version of this article (10.1186/s12870-017-1156-6) contains supplementary material, which is available to authorized users.

Molecular mechanisms underlying the diverse array of petal colors in chrysanthemum flowers

“…Recently, an expressed sequence tag database of chrysanthemum cultivar ‘Sei-Marine’ was constructed ( Sasaki et al 2017 ). Based on the database, Ohmiya et al (2017) generated a custom array and performed microarray analyses. Those authors compared the expression levels of chlorophyll-rerated genes among the white petals (absence of chlorophyll), green petals (low level of chlorophyll), and leaves (high level of chlorophyll) of chrysanthemum cultivars to identify the mechanisms of chlorophyll accumulation.…”

“…It is reasonable to assume that factors responsible for suppressing chlorophyll biosynthesis or enhancing chlorophyll degradation exist in white petals. Ohmiya et al (2017) identified several candidate transcription factors, whose expression was closely correlated with the chlorophyll level. Functional analysis of these transcription factors will provide a basis for future molecular studies on organ-specific chlorophyll accumulation.…”

“…Furthermore, application of recent advances in genetic engineering have overcome the limitations of traditional breeding and allowed the addition of novel blue/violet petal color ( Noda et al 2013 , 2017 ). These petal colors are formed by the accumulation of a single pigment, a combination of multiple pigments, such as anthocyanins, carotenoids, and chlorophylls, or absence of these pigments ( Kishimoto et al 2004 , 2007 , Nakayama et al 1997 , Ohmiya et al 2017 ).…”

Comparative transcriptome analysis provides global insight into gene expression differences between two orchid cultivars

“…STAY-GREEN protein (SGR, coded by c48794_g1) is a key component of controlling chlorophyll degeneration by destabilizing protein-pigment complexes in the thylakoid membranes [ 42 ]. In Chrysanthemums , Ohmiya et al [ 43 ] show that the expression level of SGR is drastically increased in white mutations. Zeaxanthin epoxidase (ZEP) catalyses the downstream reaction of carotenoid biosynthesis [ 44 ].…”

Extensive transcriptome changes underlying the fruit skin color intensity variation in purple eggplant

“…Almost all enzymes involved in the pathway are identi ed [18][19][20] . Several transcription factors have been reported as regulators of the chlorophyll biosynthesis pathway, such as LONG HYPOCOTYL5 (HY5), GOLDEN2-LIKE (GLK) [21][22][23] . However, limit information is available about the regulation of chlorophyll metabolism in eggplant.…”