Cytological, Biochemical, and Transcriptomic Analyses of a Novel Yellow Leaf Variation in a Paphiopedilum (Orchidaceae) SCBG COP15.

Ji Li,Lin Li,Lin Fang,Meina Wang,Kunlin Wu,Songjun Zeng

doi:10.3390/genes13010071

Abstract

The genus Paphiopedilum, belonging to the Orchidaceae, has high ornamental value. Leaf variations can considerably improve the economic and horticultural value of the orchids. In the study, a yellow leaf mutant of a Paphiopedilum hybrid named P. SCBG COP15 was identified during the in vitro plant culture process; however, little is known about their molecular mechanisms. For this, RNA-seq libraries were created and used for the transcriptomic profiling of P. SCBG COP15 and the yellow mutant. The Chl a, Chl b, and carotenoid contents in the yellow leaves decreased by approximately 75.99%, 76.92%, and 56.83%, respectively, relative to the green leaves. Decreased chloroplasts per cell and abnormal chloroplast ultrastructure were observed by electron microscopic investigation in yellowing leaves; photosynthetic characteristics and Chl fluorescence parameters were also decreased in the mutant. Altogether, 34,492 unigenes were annotated by BLASTX; 1,835 DEGs were identified, consisting of 697 upregulated and 1138 downregulated DEGs. HEMA, CRD, CAO, and CHLE, involved in Chl biosynthesis, were predicted to be key genes responsible for leaf yellow coloration. Our findings provide an essential genetic resource for understanding the molecular mechanism of leaf color variation and breeding new varieties of Paphiopedilum with increased horticultural value.

Highlights

IntroductionLeaves are vital organs in plants for photosynthesis, respiration, and nutrient transformation, as well as an important aesthetic trait in ornamental plants
Introduction published maps and institutional affilLeaves are vital organs in plants for photosynthesis, respiration, and nutrient transformation, as well as an important aesthetic trait in ornamental plants
We identified differentially expressed genes (DEGs) and transcription factors (TFs) related to Chl metabolism, and evaluated the expression levels of some key unigenes by quantitative real-time polymerase chain reaction

Summary

Introduction

Leaves are vital organs in plants for photosynthesis, respiration, and nutrient transformation, as well as an important aesthetic trait in ornamental plants. Chlorophyll (Chl), carotenoids, and anthocyanins are the main leaf pigments that are determined by genotype and growth environment [1]. Chl is the primary photosynthetic pigment found in leaves. It is able to capture light energy and transfer it to the photoreaction center to generate chemical energy during photosynthesis [2]. Most research has focused on red leaves, which are associated with anthocyanin accumulation [3]. The yellowing of leaves has received significantly less attention, and most studies on leaf yellowing have focused on Chl metabolism [4,5,6]

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