Abstract
Photosynthetic properties and transcriptomic profiles of green and white sectors of Ficus microcarpa (c.v. milky stripe fig) leaves were examined in naturally variegated plants. An anatomic analysis indicated that chloroplasts of the white sectors contained a higher abundance of starch granules and lacked stacked thylakoids. Moreover, no photosynthetic rate was detected in the white sectors. Transcriptome profile and differential expressed gene (DEG) analysis showed that genes encoding PSII core proteins were down-regulated in the white sectors. In genes related to chlorophyll metabolism, no DEGs were identified in the biosynthesis pathway of chlorophyll. However, genes encoding the first step of chlorophyll breakdown were up-regulated. The repression of genes involved in N-assimilation suggests that the white sectors were deprived of N. The mutation in the transcription factor mitochondrial transcription termination factor (mTERF) suggests that it induces colorlessness in leaves of the milky stripe fig.
Highlights
Leaf variegation is a common feature resulting from the uneven distribution or deficit of photopigments
The increment in abundance of starch granules instead of a regular lamellar structure in plastids of the non-green sectors was observed in variegated Arabidopsis [3,10,13], tobacco leaves [14], and begonia [15]
Deficiency in photosynthetic activities in the white sectors was found in the milky stripe fig (Figure 3)
Summary
Leaf variegation is a common feature resulting from the uneven distribution or deficit of photopigments. FtsHs represent another variegation-related protein family, which normally contributes to progressive protein degradation and maintenance of the thylakoid structure, with plants with loss of FtsHs functions exhibiting distorted plastids and repressed expression of photosynthetic genes in non-green sectors [5,11]. A recent transcriptomic study on chlorophyll-deficient mutant leaves of the flamingo flower (Anthurium andraeanum Lind.) showed expressional repression of transcription factors involved in chloroplast development and division [12]. Those studies of mutant lines improved our understanding of variegation and the effects of chlorophyll deficiency, research on the transcriptional profiles of naturally variegated plants is still lacking. The repression of genes related to N-assimilation and those encoding transcription factors are suggested to be the factors that induce development of white sectors
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