Characterization and bulk segregant analysis of ‘moon and star’ appearance in watermelon

The peptidoglycan (PG) layer, a core component of the bacterial cell wall, has been retained in the Physcomitrium patens chloroplasts. The PG layer entirely encompasses the P. patens chloroplast, including the division site, but how PG biosynthesis cooperates with the constriction of two envelope membranes at the chloroplast division site remains elusive. Here, focusing on the PG synthase penicillin-binding protein (PBP), we performed cytological and molecular analyses to dissect the mechanism of chloroplast division in P. patens. We showed that PBP, acting in the final step of PG biosynthesis, is likely a chloroplast inner envelope protein that can aggregate at mid-chloroplasts during chloroplast division. Physcomitrium patens had five orthologs of PLASTID DIVISION2 (PDV2), an outer envelope component of the chloroplast division complex. Our data indicated that PpPDV2 proteins interact with PpPBP and are responsible for recruiting PpPBP to the chloroplast division site, in addition to PpDRP5B. Furthermore, we found that PBP deletion and carbenicillin application restrain constriction of the chloroplast division complex, rather than its assembly. This work provides direct molecular evidence for a link between chloroplast division of P. patens and PG biosynthesis and indicates that PG biosynthesis is required for the constriction of the chloroplast division apparatus in P. patens.

The peptidoglycan synthase PBP interacts with PLASTID DIVISION2 to promote chloroplast division in Physcomitrium patens.

Chlorophyll (Chl) is an agronomic trait associated with photosynthesis and yield. Gibberellin 2-oxidases (GA2oxs) have previously been shown to be involved in Chl accumulation. However, whether and how the PbrGA2ox proteins (PbrGA2oxs) mediate Chl accumulation in pear (Pyrus spp.) is scarce.Here, we aimed to elucidate the role of the pear GA2ox gene family in Chl accumulation and the related underlying mechanisms. We isolated 13 PbrGA2ox genes (PbrGA2oxs) from the pear database and identified PbrGA2ox1 as a potential regulator of Chl accumulation. We found that transiently overexpressing PbrGA2ox1 in chlorotic pear leaves led to Chl accumulation, and PbrGA2ox1 silencing in normal pear leaves led to Chl degradation, as evident by the regreening and chlorosis phenomenon, respectively. Meanwhile, PbrGA2ox1-overexpressing (OE) tobacco plants discernably exhibited Chl built-up, as evidenced by significantly higher Pn and Fv/Fm. In addition, RNA sequencing (RNA-seq), physiological and biochemical investigations revealed an increase in abscisic acid (ABA), methyl jasmonate (MeJA), and salicylic acid (SA) concentrations and signaling pathways; a marked elevation in reducing and soluble sugar contents; and a marginal decline in the starch and sucrose levels in OE plants. Interestingly, PbrGA2ox1 overexpression did not prominently affect Chl synthesis. However, it indeed facilitated chloroplast development by increasing chloroplast number per cell and compacting the thylakoid granum stacks. These findings might jointly contribute to Chl accumulation in OE plants.Overall, our results suggested that GA2oxs accelerate Chl accumulation by stimulating chloroplast development and proved the potential of PbrGA2ox1 as a candidate gene for genetically breeding biofortified pear plants with a higher yield. 

Genome-wide identification of GA2ox genes family and analysis of PbrGA2ox1-mediated enhanced chlorophyll accumulation by promoting chloroplast development in pear

Plant cells harbor a varying number of chloroplasts, and chloroplasts multiply by division to maintain the continuity of chloroplasts. Chloroplast division is performed by the constriction of two self-assembling GTPase rings in the middle of the chloroplast: the FtsZ ring on the stromal side and the

http://www.plantphysiol.org/content/plantphysiol/182/4/1802.full.pdf

From Fuzziness to Clarity: Regulation of DRP5B Ring Dynamics at the Chloroplast Division Site.

Auxin promotes chloroplast division by increasing the expression of chloroplast division genes

Chloroplasts divide by binary fission, which is driven by a ring-like multiprotein complex spanning the inner and outer envelope membranes (OEMs) at the division site. The cytosolic DYNAMIN-RELATED PROTEIN 5B (DRP5B/ARC5) is a mechanochemical GTPase involved in binary fission of the chloroplast membrane in Arabidopsis (Arabidopsis thaliana), but the dynamics of its interactions with the chloroplast membranes and their regulation by guanine nucleotides and protein effectors remain poorly characterized. Using an Arabidopsis phot2 mutant with defects in chloroplast photorelocation movement, we determined that the ring structures of DRP5B at the chloroplast division site underwent subunit exchange with a cytosolic DRP5B pool. Mutant DRP5B proteins with impaired GTPase activity retained the ability to self-assemble at the constriction sites of chloroplasts, but did not rescue the chloroplast division defects in the Arabidopsis drp5B mutant. Our in vivo kinetic measurements of the DRP5B mutant T82D suggested that turnover of the DRP5B ring at the chloroplast division site is coupled to GTP hydrolysis. Furthermore, we established that DRP5B targeting to the chloroplast surface and assembly into a ring structure at the division site are specifically determined by the chloroplast outer OEM protein PLASTID DIVISION2 (PDV2), and that DRP5B-OEM dissociation is mainly mediated by PDV1, a paralog of PDV2. Thus, this study suggests that the mechanochemical properties of DRP5B on the chloroplast surface are dynamically regulated by its GTPase activity and major binding partners.

/pdf/pdv1-and-pdv2-differentially-affect-remodeling-and-assembly-4ddzmno0xe.pdf

PDV1 and PDV2 Differentially Affect Remodeling and Assembly of the Chloroplast DRP5B Ring

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PDV1 and PDV2 Differentially Affect Remodeling and Assembly of the Chloroplast DRP5B Ring