encoding porphobilinogen deaminase plays an important role in chlorophyll biosynthesis and function in albino var. leaves.

BACKGROUND

The chimeric leaves of var. are composed of normal green parts (Grs) and albino white parts (Whs). Although the underlying mechanism of albinism in var. leaves is not fully understood, it is likely associated with the chlorophyll (Chl) biosynthesis. In this biosynthetic process, porphobilinogen deaminase (PBGD) plays a crucial role by catalyzing the conversion of porphobilinogen (PBG) to uroporphyrinogen III (Urogen III). Therefore, its encoding gene was investigated here in association with Chl biosynthesis and albinism in chimeric var. leaves.

METHODS

The Chl content, main Chl biosynthesis precursor content, and main enzyme activity were determined and compared between the Whs and Grs of var. leaves. In addition, was cloned and its transcriptional expression and prokaryotic protein expression were analyzed. Furthermore, RNAi-mediated silencing of was produced and assessed in tobacco plants.

RESULTS

The concentration of Chl a and Chl b in the Grs was significantly higher than that in the Whs, respectively. Additionally, the content of the Chl biosynthesis precursor Urogen III decreased significantly in the Whs compared with the Grs. Thus, the transition of PBG to Urogen III may be the first rate-limiting step leading to albinism in the chimeric leaves of var. . The gene comprised 1,135 bp and was encoded into a protein with 371 amino acids; phylogenetically, was most closely related to of pineapple Prokaryotic expression and enzyme activity analysis showed that the cloned mRNA sequence of was successfully integrated and had PBGD activity. Compared with control plants, transgenic tobacco leaves with pFGC5941--RNAi vector were substantially less green with significantly reduced expression and Chl content, as well as reduced PBGD enzyme activity and significantly decreased content of Chl biosynthesis precursors from Urogen III onwards. Our results suggest that the absence of expression reduces the enzyme activity of PBGD, which blocks the transition of PBG to Urogen III, and in turn suppresses Chl synthesis leading to the pale-green leaf color. Therefore, we suggest that plays an important role in Chl synthesis and may be an important factor in the albinism of var. leaves.