Abstract
Leaf variegation is often the focus of plant breeding. Here, we studied a variegated mutant of Phalaenopsis aphrodite subsp. formosana, which is usually used as a parent of horticultural breeding, to understand its anatomic and genetic regulatory mechanisms in variegation. Chloroplasts with well-organized thylakoids and starch grains were found only in the mesophyll cells of green sectors but not of yellow sectors, confirming that the variegation belongs to the chlorophyll type. The two-dimensional electrophoresis and LC/MS/MS also reveal differential expressions of PsbP and PsbO between the green and yellow leaf sectors. Full-length cDNA sequencing revealed that mutant transcripts were caused by intron retention. When conditioning on the total RNA expression, we found that the functional transcript of PsbO and mutant transcript of PsbP are higher expressed in the yellow sector than in the green sector, suggesting that the post-transcriptional regulation of PsbO and PsbP differentiates the performance between green and yellow sectors. Because PsbP plays an important role in the stability of thylakoid folding, we suggest that the negative regulation of PsbP may inhibit thylakoid development in the yellow sectors. This causes chlorophyll deficiency in the yellow sectors and results in leaf variegation. We also provide evidence of the link of virus CymMV and the formation of variegation according to the differential expression of CymMV between green and yellow sectors.
Highlights
Foliar variegation is found in various plants
Ultrastructure of chloroplasts revealed disk-like shape with an abundance of distinct thylakoids packed into grana containing many starch grains in cells of the green sectors under the observation of Transmission Electron Microscopy (TEM) (Figure 3A)
Our TEM revealed a strong contrast in chloroplast ultrastructure between green and yellow sectors of P. aphrodite subsp. formosana plant tissue
Summary
Foliar variegation is found in various plants. This attractive trait often enhances the commercial value of ornamental plants. There are two major categories of mechanisms responsible for leaf variegation: chemical color- (pigment)-related variegation and physical color- (structural)-related variegation (Hara, 1957; Sheue et al, 2012). Formosana common chemical-color mechanisms occurring in ornamental plants, including in Ficus pumila ‘Sonny’ (Sheue et al, 2012). Pigmented-leaf variegation is derived from the formation of sectors that contain either normal-appearing chloroplasts or abnormal plastids, or other non-chlorophyll pigments (e.g., anthocyanin; Hara, 1957). Some variegated leaves of such mutants show various kinds of green and yellow sectors that are believed to originate from mutations in nuclear or organelle genes (Tilney-Bassett, 1975)
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