Physiological characterization and transcriptome analysis of a chlorosis mutant in pak choi

Abstract

Leaf color mutants are not only ideal resources for studying the physiological mechanisms of plant photosynthesis, but they are also selection markers for hybrid production. In this study, the chlorosis mutant ‘564Y’ and its wild-type counterpart ‘564’ were used to explore physiological characteristics and gene expression in pak choi. Compared with those of wild type, the dry weight and fresh weight of ‘564Y’ were significantly reduced, but the hypocotyl length of ‘564Y’ was longer. Pigment analysis showed that the chlorophyll a and carotenoid contents of ‘564Y’ were lower than those of wild type. However, there was no significant difference in chlorophyll b content between these two varieties. The photosynthetic capacity of ‘564Y’ was lower than that of ‘564’, and the photosynthetic electron transfer ability and light energy conversion efficiency were weaker in the former. Transmission electron microscopy showed that the chloroplast structure of ‘564Y’ was not compact, the thylakoid structure was irregular, and the number of matrix, grana, and stacking layers was decreased. Transcriptome analysis revealed 2958 differentially expressed genes (DEGs), and 78 gene ontology terms and 35 Kyoto Encyclopedia of Genes and Genomes pathways were significantly enriched. Among the DEGs, nine genes were associated with the chlorophyll synthesis pathway (Bra031690, Bra012595, Bra005677, Bra022628, Bra026410, Bra032155, Bra039206, Bra029875, and Bra012511) and one gene was associated with photosynthesis (Bra038011). Among these genes, 3 were identified as related to auxin metabolism too (Bra032155, Bra039206, and Bra029875). Their differential expression in the ‘564Y’ mutant and wild-type plant was confirmed by qRT-PCR. These results lay the foundation for future genetic and functional genomic studies in pak choi.