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Background  The chimeric leaves of  Ananas comosus  var.  bracteatus  are composed of normal green parts (Grs) and albino white parts (Whs). Although the underlying mechanism of albinism in  A. comosus  var.  bracteatus  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  AbhemC  was investigated here in association with Chl biosynthesis and albinism in chimeric  A. comosus  var.  bracteatus  leaves.    Methods  The Chl content, main Chl biosynthesis precursor content, and main enzyme activity were determined and compared between the Whs and Grs of  A. comosus  var.  bracteatus  leaves. In addition,  AbhemC  was cloned and its transcriptional expression and prokaryotic protein expression were analyzed. Furthermore, RNAi-mediated silencing of  AbhemC  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  A. comosus  var.  bracteatus . The gene  AbhemC  comprised 1,135 bp and was encoded into a protein with 371 amino acids; phylogenetically,  AbhemC  was most closely related to  hemC  of pineapple .  Prokaryotic expression and  in vitro  enzyme activity analysis showed that the cloned mRNA sequence of  AbhemC  was successfully integrated and had PBGD activity. Compared with control plants, transgenic tobacco leaves with pFGC5941- AbhemC -RNAi vector were substantially less green with significantly reduced  hemC  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  hemC  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  AbhemC  plays an important role in Chl synthesis and may be an important factor in the albinism of  A. comosus  var.  bracteatus  leaves.

peerj

AbhemCencoding porphobilinogen deaminase plays an important role in chlorophyll biosynthesis and function in albinoAnanas comosusvar.bracteatusleaves