Comparative physiology and transcriptome analysis provides insights into the regulatory mechanism of leaf color formation in the green and albino mutants of Bambusa oldhamii

Bamboo has a certain proportion of albinism during natural growth. Previous efforts have proved that this albinism phenotype of bamboos was determined by different genetic factors. However, the mechanism underlying albinism in most bamboo species still remains unclear. In this study, an albino mutant of Bambusa oldhamii was identified. Compared with the normal lines, the obvious degeneration in chloroplast, low chlorophyll content and reduced photosynthetic capacity were observed in albinotic leaves of B. oldhamii. However, the chloroplast genome has no difference in normal and albinotic B. oldhamii, suggesting the albino was caused by differential expressions of regulatory genes rather than gene mutations. The molecular mechanism of the albino leaves was explored through transcriptome analysis. A total of 6,191 unigenes were identified to obviously differential expressed between albino and normal lines. Most genes related to chloroplast development (including Psa, Psb etc.,), pigment biosynthesis (LHC, GUN4, ZEP etc.,) were downregulated significantly in albinotic lines, which might be the main factors responsible for albino phenotype. Moreover, some transcription factors (TFs) involved in chloroplast development and chlorophyll synthesis were also significantly upregulated (like PIF) or downregulated (like GLK1), indicating putative regulatory pathways of PIF-LHC, GLK1-LHC/Psa/Psb in albinotic B. oldhamii. Finally, downregulations of some stress responsive TFs (like ICE1, EREB1 etc.,) were found in albino leaves, suggesting a reduction in stress resistance of albinotic B. oldhamii. The above findings provided new insights into the molecular mechanism of albinism in bamboos.