Photosystem Disorder Could be the Key Cause for the Formation of Albino Leaf Phenotype in Pecan.

Ji-Yu Zhang,Tao Wang,Gang Wang,Yong-Zhi Liu,Zhan-Hui Jia,Zhong-Ren Guo

doi:10.3390/ijms21176137

Abstract

Pecan is one of the most famous nut species in the world. The phenotype of mutants with albino leaves was found in the process of seeding pecan, providing ideal material for the study of the molecular mechanisms leading to the chlorina phenotype in plants. Both chlorophyll a and chlorophyll b contents in albino leaves (ALs) were significantly lower than those in green leaves (GLs). A total of 5171 differentially expression genes (DEGs) were identified in the comparison of ALs vs. GLs using high-throughput transcriptome sequencing; 2216 DEGs (42.85%) were upregulated and 2955 DEGs (57.15%) were downregulated. The expressions of genes related to chlorophyll biosynthesis (HEMA1, encoding glutamyl-tRNA reductase; ChlH, encoding Mg-protoporphyrin IX chelatase (Mg-chelatase) H subunit; CRD, encoding Mg-protoporphyrin IX monomethylester cyclase; POR, encoding protochlorophyllide reductase) in ALs were significantly lower than those in GLs. However, the expressions of genes related to chlorophyll degradation (PAO, encoding pheophorbide a oxygenase) in ALs were significantly higher than those in GLs, indicating that disturbance of chlorophyll a biosynthesis and intensification of chlorophyll degradation lead to the absence of chlorophyll in ALs of pecan. A total of 72 DEGs associated with photosynthesis pathway were identified in ALs compared to GLs, including photosystem I (15), photosystem II (19), cytochrome b6-f complex (3), photosynthetic electron transport (6), F-type ATPase (7), and photosynthesis-antenna proteins (22). Moreover, almost all the genes (68) mapped in the photosynthesis pathway showed decreased expression in ALs compared to GLs, declaring that the photosynthetic system embedded within the thylakoid membrane of chloroplast was disturbed in ALs of pecan. This study provides a theoretical basis for elucidating the molecular mechanism underlying the phenotype of chlorina seedlings of pecan.

Highlights

Plants synthesize the carbohydrates and energy needed for growth and development through photosynthesis in leaves
The carotenoid contents in AL were significantly lower than those in green leaves (GLs) (Figure 1B), and the ratio of carotenoid/chlorophyll in AL was significantly high than that in GL (Table S1). These results suggested that albino leaves result from reduced chlorophyll levels and that the lower chlorophyll content might have resulted from abnormal chlorophyll biosynthesis and degradation
A total of 5171 differentially expression genes (DEGs) was identified in the comparison of AL vs. GL through de novo transcriptome sequencing; 2216 DEGs (42.85%) were upregulated and 2955 DEGs (57.15%) were downregulated

Summary

Introduction

Plants synthesize the carbohydrates and energy needed for growth and development through photosynthesis in leaves. The leaf color is green; leaf color variations, including chlorina, albino, red, and green leaves, with white or yellow interion, have been observed in plenty of plants, such as tea plant [1,2,3], Anthurium andraeanum [4], red maple [5], and oilseed rapa [6]. The occurrence of leaf color variations is a very complex biological process and is largely determined by genetic and environmental factors. Mutants with leaf color variations are ideal genetic material for exploring the physiological, biochemical, and molecular mechanisms of chlorophyll biosynthesis, chloroplast structure and function, and photosynthesis. Dismembering the leaf color variations’ fundamental mechanism is all-important for broadening the theoretical knowledge of plant growth and development

Methods

Results

Conclusion