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Prospective function of FtsZ proteins in the secondary plastid of chlorarachniophyte algae.

Hirakawa Y, Ishida K - BMC Plant Biol. (2015)

Bottom Line: FtsZ homologs were encoded by the nuclear genomes and carried an N-terminal plastid targeting signal.Immunoelectron microscopy revealed that both FtsZD-1 and FtsZD-2 formed a ring-like structure at the midpoint of bilobate plastids with a projecting pyrenoid in Bigelowiella natans.The ring was always associated with a shallow plate-like invagination of the two innermost plastid membranes.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8572, Japan. hirakawa.yoshi.fp@u.tsukuba.ac.jp.

ABSTRACT

Background: Division of double-membraned plastids (primary plastids) is performed by constriction of a ring-like division complex consisting of multiple plastid division proteins. Consistent with the endosymbiotic origin of primary plastids, some of the plastid division proteins are descended from cyanobacterial cell division machinery, and the others are of host origin. In several algal lineages, complex plastids, the "secondary plastids", have been acquired by the endosymbiotic uptake of primary plastid-bearing algae, and are surrounded by three or four membranes. Although homologous genes for primary plastid division proteins have been found in genome sequences of secondary plastid-bearing organisms, little is known about the function of these proteins or the mechanism of secondary plastid division.

Results: To gain insight into the mechanism of secondary plastid division, we characterized two plastid division proteins, FtsZD-1 and FtsZD-2, in chlorarachniophyte algae. FtsZ homologs were encoded by the nuclear genomes and carried an N-terminal plastid targeting signal. Immunoelectron microscopy revealed that both FtsZD-1 and FtsZD-2 formed a ring-like structure at the midpoint of bilobate plastids with a projecting pyrenoid in Bigelowiella natans. The ring was always associated with a shallow plate-like invagination of the two innermost plastid membranes. Furthermore, gene expression analysis confirmed that transcripts of ftsZD genes were periodically increased soon after cell division during the B. natans cell cycle, which is not consistent with the timing of plastid division.

Conclusions: Our findings suggest that chlorarachniophyte FtsZD proteins are involved in partial constriction of the inner pair of plastid membranes, but not in the whole process of plastid division. It is uncertain how the outer pair of plastid membranes is constricted, and as-yet-unknown mechanism is required for the secondary plastid division in chlorarachniophytes.

No MeSH data available.


Related in: MedlinePlus

Transcription of BnftsZD genes during the cell cycle. a Cell densities (cells mL−1) in the synchronized B. natans culture determined by cell counting; error bars represent standard deviations calculated based on six independent measurements. (b, c) Relative transcription levels of BnftsZD-1 and BnftsZD-2 genes detected using real-time quantitative PCR for a total of 13 time points (4 h intervals for 36 h). Each transcription level was normalized against a transcription level of the reference gene 18S rRNA. Error bars represent standard deviations of triplicate experiments
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Fig5: Transcription of BnftsZD genes during the cell cycle. a Cell densities (cells mL−1) in the synchronized B. natans culture determined by cell counting; error bars represent standard deviations calculated based on six independent measurements. (b, c) Relative transcription levels of BnftsZD-1 and BnftsZD-2 genes detected using real-time quantitative PCR for a total of 13 time points (4 h intervals for 36 h). Each transcription level was normalized against a transcription level of the reference gene 18S rRNA. Error bars represent standard deviations of triplicate experiments

Mentions: In unicellular algae with a single plastid, plastid division is generally regulated by the host cell cycle, and transcription of nucleus-encoded plastid division proteins is generally restricted to the S, G2, or M phase, when plastids divide prior to cytokinesis. Transcripts of plastidal ftsZ genes are known to accumulate during the S phase of the red alga C. merolae [48] and a couple of green algae [18], and during the S/G2 phase of the secondary plastid-bearing diatom Seminavis robusta [49]. To clarify the relationship between the timing of ftsZ gene expression and host cell division in chlorarachniophytes, we examined the transcription levels of BnftsZD genes during the cell cycle using synchronized B. natans culture. Cell division was synchronized by pretreatment of continuous light deprivation for 36 h followed by a 12:12 h light:dark cycle; cell division occurred during the second dark phase (Fig. 5a). Total RNA was extracted at 4 h intervals during the second light and dark, and third light phase, and we calculated mRNA transcription levels of BnftsZD-1 and BnftsZD-2 using real-time quantitative PCR (RT-qPCR). Transcription levels of both genes increased soon after cell division in the late dark phase (Fig. 5b, c). The transcription level of BnftsZD-1 reached a peak at the end of the dark phase corresponding to the host M/G1 phase, whereas the peak of BnftsZD-2 was 4 h before that of BnftsZD-1. Both BnFtsZ genes appeared to be regulated by the host cell cycle. Unlike other unicellular algae, however, the transcription pattern of chlorarachniophyte ftsZD genes is not consistent with the timing of plastid division that occurs before the cytokinesis. When the mRNA transcription ratio between BnftsZD-1 and BnftsZD-2 was simply calculated by Ct values of RT-qPCR at their peaks (24 h and 20 h for BnftsZD-1 and 2, respectively), the maximum transcription level of BnftsZD-1 was 2.3-fold higher than that of BnftsZD-2. This suggests that two BnFtsZD proteins might exist in the plastids in different molecular amounts.Fig. 5


Prospective function of FtsZ proteins in the secondary plastid of chlorarachniophyte algae.

Hirakawa Y, Ishida K - BMC Plant Biol. (2015)

Transcription of BnftsZD genes during the cell cycle. a Cell densities (cells mL−1) in the synchronized B. natans culture determined by cell counting; error bars represent standard deviations calculated based on six independent measurements. (b, c) Relative transcription levels of BnftsZD-1 and BnftsZD-2 genes detected using real-time quantitative PCR for a total of 13 time points (4 h intervals for 36 h). Each transcription level was normalized against a transcription level of the reference gene 18S rRNA. Error bars represent standard deviations of triplicate experiments
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4641359&req=5

Fig5: Transcription of BnftsZD genes during the cell cycle. a Cell densities (cells mL−1) in the synchronized B. natans culture determined by cell counting; error bars represent standard deviations calculated based on six independent measurements. (b, c) Relative transcription levels of BnftsZD-1 and BnftsZD-2 genes detected using real-time quantitative PCR for a total of 13 time points (4 h intervals for 36 h). Each transcription level was normalized against a transcription level of the reference gene 18S rRNA. Error bars represent standard deviations of triplicate experiments
Mentions: In unicellular algae with a single plastid, plastid division is generally regulated by the host cell cycle, and transcription of nucleus-encoded plastid division proteins is generally restricted to the S, G2, or M phase, when plastids divide prior to cytokinesis. Transcripts of plastidal ftsZ genes are known to accumulate during the S phase of the red alga C. merolae [48] and a couple of green algae [18], and during the S/G2 phase of the secondary plastid-bearing diatom Seminavis robusta [49]. To clarify the relationship between the timing of ftsZ gene expression and host cell division in chlorarachniophytes, we examined the transcription levels of BnftsZD genes during the cell cycle using synchronized B. natans culture. Cell division was synchronized by pretreatment of continuous light deprivation for 36 h followed by a 12:12 h light:dark cycle; cell division occurred during the second dark phase (Fig. 5a). Total RNA was extracted at 4 h intervals during the second light and dark, and third light phase, and we calculated mRNA transcription levels of BnftsZD-1 and BnftsZD-2 using real-time quantitative PCR (RT-qPCR). Transcription levels of both genes increased soon after cell division in the late dark phase (Fig. 5b, c). The transcription level of BnftsZD-1 reached a peak at the end of the dark phase corresponding to the host M/G1 phase, whereas the peak of BnftsZD-2 was 4 h before that of BnftsZD-1. Both BnFtsZ genes appeared to be regulated by the host cell cycle. Unlike other unicellular algae, however, the transcription pattern of chlorarachniophyte ftsZD genes is not consistent with the timing of plastid division that occurs before the cytokinesis. When the mRNA transcription ratio between BnftsZD-1 and BnftsZD-2 was simply calculated by Ct values of RT-qPCR at their peaks (24 h and 20 h for BnftsZD-1 and 2, respectively), the maximum transcription level of BnftsZD-1 was 2.3-fold higher than that of BnftsZD-2. This suggests that two BnFtsZD proteins might exist in the plastids in different molecular amounts.Fig. 5

Bottom Line: FtsZ homologs were encoded by the nuclear genomes and carried an N-terminal plastid targeting signal.Immunoelectron microscopy revealed that both FtsZD-1 and FtsZD-2 formed a ring-like structure at the midpoint of bilobate plastids with a projecting pyrenoid in Bigelowiella natans.The ring was always associated with a shallow plate-like invagination of the two innermost plastid membranes.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8572, Japan. hirakawa.yoshi.fp@u.tsukuba.ac.jp.

ABSTRACT

Background: Division of double-membraned plastids (primary plastids) is performed by constriction of a ring-like division complex consisting of multiple plastid division proteins. Consistent with the endosymbiotic origin of primary plastids, some of the plastid division proteins are descended from cyanobacterial cell division machinery, and the others are of host origin. In several algal lineages, complex plastids, the "secondary plastids", have been acquired by the endosymbiotic uptake of primary plastid-bearing algae, and are surrounded by three or four membranes. Although homologous genes for primary plastid division proteins have been found in genome sequences of secondary plastid-bearing organisms, little is known about the function of these proteins or the mechanism of secondary plastid division.

Results: To gain insight into the mechanism of secondary plastid division, we characterized two plastid division proteins, FtsZD-1 and FtsZD-2, in chlorarachniophyte algae. FtsZ homologs were encoded by the nuclear genomes and carried an N-terminal plastid targeting signal. Immunoelectron microscopy revealed that both FtsZD-1 and FtsZD-2 formed a ring-like structure at the midpoint of bilobate plastids with a projecting pyrenoid in Bigelowiella natans. The ring was always associated with a shallow plate-like invagination of the two innermost plastid membranes. Furthermore, gene expression analysis confirmed that transcripts of ftsZD genes were periodically increased soon after cell division during the B. natans cell cycle, which is not consistent with the timing of plastid division.

Conclusions: Our findings suggest that chlorarachniophyte FtsZD proteins are involved in partial constriction of the inner pair of plastid membranes, but not in the whole process of plastid division. It is uncertain how the outer pair of plastid membranes is constricted, and as-yet-unknown mechanism is required for the secondary plastid division in chlorarachniophytes.

No MeSH data available.


Related in: MedlinePlus