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Research of photosynthesis and genomewide resequencing on a yellow-leaf Lotus japonicus
 mutant induced by carbon ion beam irradiation

Carbon ion beam is an advanced physical mutagen that is used for mutation breeding and functional genomics research. Using carbon ion beams, a stable Lotus japonicus mutant C16 which showed yellow leaves and reduced height compared with the laboratory wild type was obtained in our previous study. Yellow‐leaf mutation is a desirable characteristic for studying photosynthesis. The photosynthetic‐related physiological indexes, including the content of chlorophylls and the ratio of variable fluorescence (Fᵥ) over the maximum fluorescence value (Fₘ) (maximal photochemical efficiency of photosystem II in the dark) of leaves between laboratory wild type and C16, were investigated. C16 showed lower amount of chlorophylls than that of laboratory wild type, as well as a relatively photosynthetic capacity. Meanwhile, to comprehend the molecular mechanism underlying the mutant, genomewide resequencing was performed to identify the mutational site responsible for the yellow‐leaf phenotype causing the weaker photosynthetic capacity. Ninety‐five single‐base substitutions and 17 small insertions and deletions were found in C16 mutant. Among those, by association analysis of functional annotation and mutant phenotype, T>G SBS in chromosome 5 located in Lj5g3v1669360.1 which encodes arabinogalactan protein was supposed as candidate mutation sites. Quantitative real‐time polymerase chain reaction analysis indicated that the expression level of Lj5g3v1669360.1 in C16 was significantly lower than that of laboratory wild type. Decreased expression of the Lj5g3v1669360.1 may be responsible for the smaller amount of chlorophylls causing yellow leaves, the weaker photosynthetic capacity of C16, and resulting in slow growth.