Abstract
Populus deltoides Marsh has high ornamental value because its leaves remain yellow during the non-dormant period. However, little is known about the regulatory mechanism of leaf coloration in P. deltoides Marsh. Thus, we analyzed the physiological and transcriptional differences of yellow leaves (mutant) and green leaves (wild-type) of P. deltoides Marsh. Physiological experiments showed that the contents of chlorophyll (Chl) and carotenoid were lower in mutant leaves, and the flavonoid content did not differ significantly between mutant and wild-type leaves. Transcriptomic sequencing was further used to identify 153 differentially expressed genes (DEGs). Functional classifications based on Gene Ontology enrichment and Genome enrichment analysis indicated that the DEGs were involved in Chl biosynthesis and flavonoid biosynthesis pathways. Among these, geranylgeranyl diphosphate (CHLP) genes associated with Chl biosynthesis showed down-regulation, while chlorophyllase (CLH) genes associated with Chl degradation were up-regulated in yellow leaves. The expression levels of these genes were further confirmed using quantitative real-time PCR (RT-qPCR). Furthermore, the estimation of the main precursors of Chl confirmed that CHLP is a vital enzyme for the yellow leaf color phenotype. Consequently, the formation of yellow leaf color is due to the disruption of Chl synthesis or catabolism rather than flavonoid synthesis. These results contribute to our understanding of mechanisms and regulation of leaf color variation in poplar at the transcriptional level.
Highlights
Leaf color is an important feature of ornamental plants, and trees with colored leaves have been widely cultivated in landscape gardens
The uroporphyrinogen III (Urogen III) content of the yellow leaves was significantly higher than that of the wild-type, whereas there were no significant differences in coproporphyrinogen III
Further detailed analysis showed that the protoporphyrin IX (Proto IX), magnesium protoporphyrin IX (Mg-Proto IX) and protochlorophyllide (Pchlide) contents of the mutant were significantly decreased by about 52.53%-64.71% than those from green leaves
Summary
Leaf color is an important feature of ornamental plants, and trees with colored leaves have been widely cultivated in landscape gardens. The main factors that determine foliage color are the types of pigment and their relative concentrations. The formation of red leaves is the result of anthocyanin accumulation, which has been extensively studied [1]. There are only a few studies focus on the mechanism of yellow leaves. Leaf yellowing is generally considered to be caused by decreased Chl content, since Chl is the main pigment content of green leaves [2]. Studies of leaf yellowing have mostly focused on Chl biosynthesis and degradation. Leaf yellowing may be due to the accumulation of flavonoids such as flavanol, flavonol, chalcone, aurone [3,4]
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