Unlocking the secrets of chimerism: Plastid genes and the quest for variegation in the ornamental plant market
image: Chimeric plant materials and variation in their plastomes between green and albino sectors. a, Representative chimeric leaves of the 14 plants with plastome polymorphisms identified in this study.
Credit: Horticulture Research
The global indoor plant market is burgeoning, with projections of reaching $7.27 billion by 2025. Chimeric plants, first noted in the 17th century, have become popular for their distinctive variegated patterns. These patterns are a product of the structure and development of the plant's shoot apical meristem (SAM). Recent studies have shown that chimeric plants, displaying both normal and albino tissues, often result from mutations in the plastome, the genetic material in chloroplasts responsible for photosynthesis. These mutations affect plastid gene transcription, regulated by two types of RNA polymerases, leading to diverse phenotypic expressions. However, the precise genetic triggers and regulation of chimerism are still unknown.
In November 2022, Horticulture Research published a perspective entitled by “High-throughput discovery of plastid genes causing albino phenotypes in ornamental chimeric plants”.
In this study, researchers examined 23 chimeric plants from various species and reconstructed their plastomes de novo using a method involving genomic DNA sequencing of green leaf tissue (GLT) and albino leaf tissue (ALT). These results revealed a quadripartite structure in angiosperm plastomes and a lack of inverted repeats in gymnosperm plastomes. Crucially, the study found heteroplasmy in 14 out of 23 plants, with variances in plastomes derived from GLT and ALT being attributed to single point mutations. No nuclear ribosomal DNA differences were observed between GLT and ALT. Subsequent analysis of the plastomes identified 14 independent genic mutations across eight plastid genes, and confirmed that each mutation would disrupt certain aspects of chloroplast function, leading to albino zones or leaves. Furthermore, a notable contrast emerged in the sequencing reads of wild-type and mutant plastomes between GLT and ALT, with mutations predominantly found in the ALT plastomes, suggesting a disruption in chloroplast function. Delving into the functional implications, the RpoC2 mutation discovered in R. japonica's albino leaves was characterized. Structural analyses, using protein modeling and comparison with a bacterial RNA polymerase, indicated that the mutation likely affects the structural integrity and function of the enzyme. Transcriptional analysis confirmed the impact of this mutation, with a marked decrease in the expression of photosystem-related genes in ALT. Further research results indicated that the photosystem cannot form correctly in ALT, and the substitution of RpoC2 His114Pro in ALT plastids may impair the correct transcription of photosynthetic genes, thereby affecting photosynthesis in albino tissues.
In conclusion, this study not only identified specific mutations linked to the albino phenotype in chimeric plants but also shed light on the significant role of these mutations in compromising the plants' photosynthetic machinery. These findings are critical and lay the foundation for future research aimed at understanding plastid biogenesis and the evolution of organellar genomes, thus potentially leading to the advancement of horticultural practices and genetic engineering for variegated plant varieties.
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References
Authors
Hyun-Seung Park1,2,†, Jae-Hyeon Jeon1,†, Woohyeon Cho1,†, Yeonjeong Lee1,†, Jee Young Park1, Jiseok Kim1, Young Sang Park1, Hyun Jo Koo1, Jung Hwa Kang3, Taek Joo Lee3, Sang Hoon Kim4, Jin-Baek Kim4, Hae-Yun Kwon5, Suk-Hwan Kim1, Nam-Chon Paek1, Geupil Jang6, Jeong-Yong Suh7 and Tae-Jin Yang1,*
†These four authors contributed equally
Affiliations
1. Department of Agriculture, Forestry and Bioresources, Research Institute of Agriculture and Life Sciences, and Plant Genomics and Breeding Institute, College of Agriculture and Life Sciences, Seoul National University, Seoul, 08826, Republic of Korea
2. Department of Integrative Biological Sciences and Industry, Sejong University, Seoul 05006, Korea
3. Hantaek Botanical Garden, Yongin, Gyeonggi-do, 17183, Republic of Korea
4. Radiation Breeding Research Team, Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeongeup 56212, Korea
5. Special Forest Resources Division, National Institute of Forest Science, Suwon 16631, Korea
6. School of Biological Sciences and Technology, Chonnam National University, Gwangju, South Korea
7. Department of Agricultural Biotechnology and Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea
About Tae-Jin Yang
He is a professor in the Department of Agriculture, Forestry and Bioresources of College of Agriculture and Life Sciences at Seoul National University. He was one of ten recipients of the 2020 SNU Excellence in Research Award. He has published 210 research papers in the field of genomics and medicinal plants, and was first in the world to successfully analyze the ginseng genome.