@article{MeridaFettke2021,
  author    = {Merida, Angel and Fettke, J{\"o}rg},
  title     = {Starch granule initiation in Arabidopsis thaliana chloroplasts},
  series = {The plant journal},
  volume    = {107},
  journal   = {The plant journal},
  number    = {3},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {0960-7412},
  doi       = {10.1111/tpj.15359},
  pages     = {688 -- 697},
  year      = {2021},
  abstract  = {The initiation of starch granule formation and the mechanism controlling the number of granules per plastid have been some of the most elusive aspects of starch metabolism. This review covers the advances made in the study of these processes. The analyses presented herein depict a scenario in which starch synthase isoform 4 (SS4) provides the elongating activity necessary for the initiation of starch granule formation. However, this protein does not act alone; other polypeptides are required for the initiation of an appropriate number of starch granules per chloroplast. The functions of this group of polypeptides include providing suitable substrates (maltooligosaccharides) to SS4, the localization of the starch initiation machinery to the thylakoid membranes, and facilitating the correct folding of SS4. The number of starch granules per chloroplast is tightly regulated and depends on the developmental stage of the leaves and their metabolic status. Plastidial phosphorylase (PHS1) and other enzymes play an essential role in this process since they are necessary for the synthesis of the substrates used by the initiation machinery. The mechanism of starch granule formation initiation in Arabidopsis seems to be generalizable to other plants and also to the synthesis of long-term storage starch. The latter, however, shows specific features due to the presence of more isoforms, the absence of constantly recurring starch synthesis and degradation, and the metabolic characteristics of the storage sink organs.},
  language  = {en}
}
@article{WangLiMaetal.2021,
  author    = {Wang, Meng and Li, Panpan and Ma, Yao and Nie, Xiang and Grebe, Markus and Men, Shuzhen},
  title     = {Membrane sterol composition in Arabidopsis thaliana affects root elongation via auxin biosynthesis},
  series = {International journal of molecular sciences},
  volume    = {22},
  journal   = {International journal of molecular sciences},
  number    = {1},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {1422-0067},
  doi       = {10.3390/ijms22010437},
  pages     = {20},
  year      = {2021},
  abstract  = {Plant membrane sterol composition has been reported to affect growth and gravitropism via polar auxin transport and auxin signaling. However, as to whether sterols influence auxin biosynthesis has received little attention. Here, by using the sterol biosynthesis mutant cyclopropylsterol isomerase1-1 (cpi1-1) and sterol application, we reveal that cycloeucalenol, a CPI1 substrate, and sitosterol, an end-product of sterol biosynthesis, antagonistically affect auxin biosynthesis. The short root phenotype of cpi1-1 was associated with a markedly enhanced auxin response in the root tip. Both were neither suppressed by mutations in polar auxin transport (PAT) proteins nor by treatment with a PAT inhibitor and responded to an auxin signaling inhibitor. However, expression of several auxin biosynthesis genes TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1 (TAA1) was upregulated in cpi1-1. Functionally, TAA1 mutation reduced the auxin response in cpi1-1 and partially rescued its short root phenotype. In support of this genetic evidence, application of cycloeucalenol upregulated expression of the auxin responsive reporter DR5:GUS (beta-glucuronidase) and of several auxin biosynthesis genes, while sitosterol repressed their expression. Hence, our combined genetic, pharmacological, and sterol application studies reveal a hitherto unexplored sterol-dependent modulation of auxin biosynthesis during Arabidopsis root elongation.},
  language  = {en}
}
@article{LiuLiFettke2021,
  author    = {Liu, Qingting and Li, Xiaoping and Fettke, J{\"o}rg},
  title     = {Starch granules in Arabidopsis thaliana mesophyll and guard cells show similar morphology but differences in size and number},
  series = {International journal of molecular sciences},
  volume    = {22},
  journal   = {International journal of molecular sciences},
  number    = {11},
  publisher = {Molecular Diversity Preservation International},
  address   = {Basel},
  issn      = {1422-0067},
  doi       = {10.3390/ijms22115666},
  pages     = {11},
  year      = {2021},
  abstract  = {Transitory starch granules result from complex carbon turnover and display specific situations during starch synthesis and degradation. The fundamental mechanisms that specify starch granule characteristics, such as granule size, morphology, and the number per chloroplast, are largely unknown. However, transitory starch is found in the various cells of the leaves of Arabidopsis thaliana, but comparative analyses are lacking. Here, we adopted a fast method of laser confocal scanning microscopy to analyze the starch granules in a series of Arabidopsis mutants with altered starch metabolism. This allowed us to separately analyze the starch particles in the mesophyll and in guard cells. In all mutants, the guard cells were always found to contain more but smaller plastidial starch granules than mesophyll cells. The morphological properties of the starch granules, however, were indiscernible or identical in both types of leaf cells.},
  language  = {en}
}
@article{LiuZhouFettke2021,
  author    = {Liu, Qingting and Zhou, Yuan and Fettke, J{\"o}rg},
  title     = {Starch granule size and morphology of Arabidopsis thaliana starch-related mutants analyzed during diurnal rhythm and development},
  series = {Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International},
  volume    = {26},
  journal   = {Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International},
  edition   = {19},
  publisher = {MDPI},
  address   = {Basel, Schweiz},
  issn      = {1420-3049},
  doi       = {10.3390/molecules26195859},
  pages     = {1 -- 9},
  year      = {2021},
  abstract  = {Transitory starch plays a central role in the life cycle of plants. Many aspects of this important metabolism remain unknown; however, starch granules provide insight into this persistent metabolic process. Therefore, monitoring alterations in starch granules with high temporal resolution provides one significant avenue to improve understanding. Here, a previously established method that combines LCSM and safranin-O staining for in vivo imaging of transitory starch granules in leaves of Arabidopsis thaliana was employed to demonstrate, for the first time, the alterations in starch granule size and morphology that occur both throughout the day and during leaf aging. Several starch-related mutants were included, which revealed differences among the generated granules. In ptst2 and sex1-8, the starch granules in old leaves were much larger than those in young leaves; however, the typical flattened discoid morphology was maintained. In ss4 and dpe2/phs1/ss4, the morphology of starch granules in young leaves was altered, with a more rounded shape observed. With leaf development, the starch granules became spherical exclusively in dpe2/phs1/ss4. Thus, the presented data provide new insights to contribute to the understanding of starch granule morphogenesis.},
  language  = {en}
}