The Plant Journal

doi: 10.1111/tpj.12989pmid: N/A

Kobbe, Daniela; Kahles, Andy; Walter, Maria; Klemm, Tobias; Mannuss, Anja; Knoll, Alexander; Focke, Manfred; Puchta, Holger

doi: 10.1111/tpj.13283pmid: 27458713

DNA lesions such as crosslinks represent obstacles for the replication machinery. Nonetheless, replication can proceed via the DNA damage tolerance pathway also known as postreplicative repair pathway. SNF2 ATPase Rad5 homologs, such as RAD5A of the model plant Arabidopsis thaliana, are important for the error‐free mode of this pathway. We able to demonstrate before, that RAD5A is a key factor in the repair of DNA crosslinks in Arabidopsis. Here, we show by in vitro analysis that AtRAD5A protein is a DNA translocase able to catalyse fork regression. Interestingly, replication forks with a gap in the leading strand are processed best, in line with its suggested function. Furthermore AtRAD5A catalyses branch migration of a Holliday junction and is furthermore not impaired by the DNA binding of a model protein, which is indicative of its ability to displace other proteins. Rad5 homologs possess HIRAN (Hip116, Rad5; N‐terminal) domains. By biochemical analysis we were able to demonstrate that the HIRAN domain variant from Arabidopsis RAD5A mediates structure selective DNA binding without the necessity for a free 3′OH group as has been shown to be required for binding of HIRAN domains in a mammalian RAD5 homolog. The biological importance of the HIRAN domain in AtRAD5A is demonstrated by our result that it is required for its function in DNA crosslink repair in vivo.

Steiner, Alexander; Rybak, Katarzyna; Altmann, Melina; McFarlane, Heather E.; Klaeger, Susan; Nguyen, Ngoc; Facher, Eva; Ivakov, Alexander; Wanner, Gerhard; Kuster, Bernhard; Persson, Staffan; Braun, Pascal; Hauser, Marie‐Theres; Assaad, Farhah F.

Van Aken, Olivier; Ford, Ethan; Lister, Ryan; Huang, Shaobai; Millar, A.Harvey

doi: 10.1111/tpj.13276pmid: 27425258

Mitochondria are crucial for plant viability and are able to communicate information on their functional status to the cellular nucleus via retrograde signalling, thereby affecting gene expression. It is currently unclear if retrograde signalling in response to constitutive mitochondrial biogenesis defects is mediated by the same pathways as those triggered during acute mitochondrial dysfunction. Furthermore, it is unknown if retrograde signalling can effectively improve plant performance when mitochondrial function is constitutively impaired. Here we show that retrograde signalling in mutants defective in mitochondrial proteins RNA polymerase rpotmp or prohibitin atphb3 can be suppressed by knocking out the transcription factor ANAC017. Genome‐wide RNA‐seq expression analysis revealed that ANAC017 is almost solely responsible for the most dramatic transcriptional changes common to rpotmp and atphb3 mutants, regulating classical marker genes such as alternative oxidase 1a (AOX1a) and also previously‐uncharacterised DUF295 genes that appear to be new retrograde markers. In contrast, ANAC017 does not regulate intra‐mitochondrial gene expression or transcriptional changes unique to either rpotmp or atphb3 genotype, suggesting the existence of currently unknown signalling cascades. The data show that ANAC017 function extends beyond common retrograde transcriptional responses and affects downstream protein abundance and enzyme activity of alternative oxidase, as well as steady‐state energy metabolism in atphb3 plants. Furthermore, detailed growth analysis revealed that ANAC017‐dependent retrograde signalling provides benefits for growth and productivity in plants with mitochondrial defects. In conclusion, ANAC017 plays a key role in both biogenic and operational mitochondrial retrograde signalling, and improves plant performance when mitochondrial function is constitutively impaired.

Yunus, Ian Sofian; Liu, Yu‐chi; Nakamura, Yuki

doi: 10.1111/tpj.13278pmid: 27436233

In plants, ethanolamine is considered a precursor for the synthesis of choline, which is an essential dietary nutrient for animals. An enzyme serine decarboxylase (SDC) has been identified and characterized in Arabidopsis, which directly converts serine to ethanolamine, a precursor to phosphorylethanolamine and its subsequent metabolites in plants. However, the importance of SDC and ethanolamine production in plant growth and development remains unclear. Here, we show that SDC is required for ethanolamine biosynthesis in vivo and essential in plant embryogenesis in Arabidopsis. The knockout of SDC1 caused an embryonic lethal defect due to the developmental arrest of the embryos at the heart stage. During embryo development, the expression was observed at the later stages, at which developmental defect occurred in the knockout mutant. Overexpression of SDC1 in planta increased levels of ethanolamine, phosphatidylethanolamine, and phosphatidylcholine both in leaves and siliques. These results suggest that SDC1 plays an essential role in ethanolamine biosynthesis during the embryogenesis in Arabidopsis.

Czesnick, Hjördis; Lenhard, Michael

doi: 10.1111/tpj.13280pmid: 27447095

Polyadenylation is a critical 3′‐end processing step during maturation of pre‐mRNAs, and the length of the poly(A) tail affects mRNA stability, nuclear export and translation efficiency. The Arabidopsis thaliana genome encodes three canonical nuclear poly(A) polymerase (PAPS) isoforms fulfilling specialized functions, as reflected by their different mutant phenotypes. While PAPS1 affects several processes, such as the immune response, organ growth and male gametophyte development, the roles of PAPS2 and PAPS4 are largely unknown. Here we demonstrate that PAPS2 and PAPS4 promote flowering in a partially redundant manner. The enzymes act antagonistically to PAPS1, which delays the transition to flowering. The opposite flowering‐time phenotypes in paps1 and paps2 paps4 mutants are at least partly due to decreased or increased FLC activity, respectively. In contrast to paps2 paps4 mutants, plants with increased PAPS4 activity flower earlier than the wild‐type, concomitant with reduced FLC expression. Double mutant analyses suggest that PAPS2 and PAPS4 act independently of the autonomous pathway components FCA, FY and CstF64. The direct polyadenylation targets of the three PAPS isoforms that mediate their effects on flowering time do not include FLC sense mRNA and remain to be identified. Thus, our results uncover a role for canonical PAPS isoforms in flowering‐time control, raising the possibility that modulating the balance of the isoform activities could be used to fine tune the transition to flowering.

Li, Qing; Fang, Chao; Duan, Zongbiao; Liu, Yucheng; Qin, Hao; Zhang, Jixiang; Sun, Peng; Li, Wenbin; Wang, Guodong; Tian, Zhixi

doi: 10.1111/tpj.13282pmid: 27459730

Polyploidy is prevalent in nature. As the fate of duplicated genes becomes more complicated when the encoded proteins function as oligomers, functional investigations into duplicated oligomer‐encoding genes in polyploid genomes will facilitate our understanding of how traits are expressed. In this study, we identified GmCHLI1, a gene encoding the I subunit of magnesium (Mg)‐chelatase, which functions in hexamers as responsible for the semi‐dominant etiolation phenotype in soybean. Four GmCHLI copies derived from two polyploidy events were identified in the soybean genome. Further investigation with regard to expression patterns indicated that these four copies have diverged into two pairs; mutation in the other copy of the pair that includes GmCHLI1 also resulted in a chlorophyll‐deficient phenotype. Protein interaction assays showed that these four GmCHLIs can interact with each other, but stronger interactions were found with mutated subunits. The results indicate that, in polyploidy, deficiency in each copy of duplicated oligomer‐encoding genes could result in a mutant phenotype due to hetero‐oligomer formation, which is different from the model of allelic dosage or functional redundancy. In addition, we interestingly found an increase in isoflavonoids in the heterozygous etiolated plants, which might be useful for improving soybean seed quality.

Zhu, Anyu; Greaves, Ian K.; Liu, Pei‐Chuan; Wu, Limin; Dennis, Elizabeth S.; Peacock, W. James

doi: 10.1111/tpj.13285pmid: 27460790

Hybrid vigour (heterosis) has been used for decades in crop industries, especially in the production of maize and rice. Hybrid varieties usually exceed their parents in plant biomass and seed yield. But the molecular basis of hybrid vigour is not fully understood. In this project, we studied heterosis at early stages of seedling development in Arabidopsis hybrids derived from crossing Ler and C24 accessions. We found that early heterosis is associated with non‐additive gene expression that resulted from earlier changes in gene expression in the hybrids relative to the parents. The non‐additively expressed genes are involved in metabolic pathways, including photosynthesis, critical for plant growth. The early increased expression levels of genes involved in energy production in hybrids is associated with heterosis in the young seedlings that could be essential for biomass heterosis at later developmental stages of the plant.

Chen, Hu‐hui; Chu, Pu; Zhou, Yu‐liang; Ding, Yu; Li, Yin; Liu, Jun; Jiang, Li‐wen; Huang, Shang‐zhi

doi: 10.1111/tpj.13286pmid: 27464651

Seed longevity, the maintenance of viability during storage, is a major factor for conservation of genetic resources and biodiversity. Seed longevity is an important trait of agriculture crop and is impaired by reactive oxygen species (ROS) during seed desiccation, storage and germination (C. R. Biol., 331, 2008 and 796). Seeds possess a wide range of systems (protection, detoxification, repair) allowing them to survive during storage and to preserve a high germination ability. In many plants, 1‐cys peroxiredoxin (1‐Cys Prx, also named PER1) is a seed‐specific antioxidant which eliminates ROS with cysteine residues. Here we identified and characterized a seed‐specific PER1 protein from seeds of sacred lotus (Nelumbo nucifera Gaertn.). Purified NnPER1 protein protects DNA against the cleavage by ROS in the mixed‐function oxidation system. The transcription and protein accumulation of NnPER1 increased during seed desiccation and imbibition and under abiotic stress treatment. Ectopic expression of NnPER1 in Arabidopsis enhanced the seed germination ability after controlled deterioration treatment (CDT), indicating that NnPER1 improves seed longevity of transgenic plants. Consistent with the function of NnPER1 on detoxifying ROS, we found that the level of ROS release and lipid peroxidation was strikingly lower in transgenic seeds compared to wild‐type with or without CDT. Furthermore, transgenic Arabidopsis seeds ectopic‐expressing NnPER1 displayed enhanced tolerance to high temperature and abscisic acid (ABA), indicating that NnPER1 may participate in the thermotolerance and ABA signaling pathway.

Song, Longzhen; Wang, Ruci; Zhang, Li; Wang, Yueming; Yao, Shanguo

doi: 10.1111/tpj.13287pmid: 27464824

The ovary of rice undergoes rapid expansion immediately after fertilization, and this process determines the final sink strength potential of caryopses. To date, work on rice grain development has mainly focused on endosperm filling, whereas information on the essential elements for ovary expansion remains limited. We report here a functional analysis of the ovary expansion retarded mutant crr1 in rice. Map‐based cloning revealed that CRR1 encodes a protein homologous to the Arabidopsis callose synthases AtGSL8 and AtGSL10. Point mutation in crr1 resulted in alternative splicing, which led to the formation of the truncated crr1 protein without the β‐glucan synthase domain. Iodine staining showed that there were few starch granules and these were unevenly distributed in the pericarp of crr1, and a 5,6‐carboxyfluorescein diacetate transport assay revealed that carbohydrates were less efficiently unloaded from the lateral vasculature into the developing caryopsis. CRR1 transcripts were detected in all plant organs, with the highest level found in receptacles, which are mainly composed of vascular tissues. Analysis of pCRR1::GUS transgenic plants showed that CRR1 was specifically expressed in vascular bundle cells. Consistently, loss of function of CRR1 led to disordered patterns of vascular cells in the ovaries and receptacles of the mutant. Furthermore, a small portion of cells in the vascular bundles of crr1 showed defective cell wall formation, and callose deposition was specifically reduced at the plasmodesmata (PD) of cells with aberrant walls. Our results suggest that CRR1 performs a pivotal role in determining initial ovary expansion in rice, possibly via the PD‐mediated permeability of cell fate determinants for vascular cell differentiation.