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Embryo development is essential for seed yield and post-germination growth. Glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in oxidative pentose phosphate pathway (OPPP), is widely involved in plant development and stress tolerance by providing nicotinamide adenine dinucleotide phosphate (NADPH). In this study, the double mutant (g6pd5/6), overexpression line (G6PD5/6OE) and complementation line (g6pd5/6 Comp) of cytosolic glucose-6-phosphate dehydrogenases (Cyt-G6PD) were used to investigate Cyt-G6PD roles in embryo development of Arabidopsis. The results showed that the germination rate of g6pd5/6 seeds was delayed in comparison with that of Col-0; moreover, 11.5% of g6pd5/6 seeds did not germinate. The dysfunction of Cyt-G6PD resulted in decreased fresh weight and primary root length of g6pd5/6 seedlings. The height and silique length of g6pd5/6 plants were also decreased. Moreover, the abortion rate of siliques and seeds of g6pd5/6 plants were increased compared with those of Col-0, G6PD5/6OE and g6pd5/6 Comp lines. However, the dysfunction of Cyt-G6PD did not affect pollen activity; but in g6pd5/6 , the embryo development was partially delayed or inhibited. The contents of fatty acids and storage proteins, two main storage materials in Arabidopsis seeds, were decreased in g6pd5/6 seeds. Exogenous application of fatty acids (C18:2; C18:3) alleviated the delayed germination of g6pd5/6 seeds. RT-qPCR results further demonstrated that the early embryo development genes were down-regulated in g6pd5/6. Taken together, Cyt-G6PD plays a pivotal role in plant seed development by regulating the transcriptions of early embryo development genes and the accumulation of storage materials (especially fatty acids). • Cyt-G6PD mutation affects the transcription of genes involved in embryonic development in Arabidopsis. • Cyt-G6PD mutation decreases the contents of fatty acids and storage proteins in g6pd5/6 seeds. • Cyt-G6PD dysfunction reduces seed yield and delays post-embryonic development of Arabidopsis seedlings. [ABSTRACT FROM AUTHOR]

Seed germination is a critical checkpoint for plant survival under stresses, which requires functional mitochondria for energy and signal supply. Mitochondrial ALTERNATIVE OXIDASE 2 (AOX2) is specifically and highly expressed at early seed germination; however, its regulatory mechanism remains unknown. Here, the mutant (aox2), over-expression (AOX2 OE) and complementation (aox2 Comp , proAOX2::gAOX2/aox2) lines were used to investigate AOX2 roles. AOX2 transcript was significantly up-regulated under ABA, NaCl, H 2 O 2 , PEG6000 or mannitol treatments during seed germination. Compared with WT and aox2 Comp , seed germination and greening were delayed in aox2 under NaCl treatment but enhanced in AOX2 OE lines. The transcripts of key genes related to ABA biosynthesis and signal transduction were up-regulated in aox2 compared with those in WT under salt stress. Consequently, the higher ABA level was found in aox2. Na 2 WO 4 , the inhibitor of ABA biosynthesis, significantly enhanced germination rate of aox2. Mutation of ABA-INSENSITIVE 3 (ABI3) or ABI4 can partially reverse the salt-sensitive phenotypes of aox2. Yeast one-hybrid, D-luciferin enzyme (LUC) assay and transient expression experiments further revealed ABI3 and ABI4 can directly interact with AOX2 promoter and enhance its expression. Reactive oxygen species (ROS), mainly produced from the root tip mitochondria of germinated seeds, were accumulated more in aox2 than those in WT. Exogenous ascorbic acid (AsA) decreased ROS level and fully rescued the salt-hypersensitive phenotypes of aox2. Taken together, AOX2 plays an important role in Arabidopsis seed germination through regulating ABA signal and ROS homeostasis under salt stress; in the process, ABI3/ABI4 is indispensable for salinity-induced AOX2 expression. • AOX2 plays an important role in Arabidopsis seed germination. • AOX2 modulates seed germination through regulating ABA signal and mitochondrial ROS homeostasis under salt stress. • ABI3 and ABI4 are indispensable for salinity-induced AOX2 transcription. [ABSTRACT FROM AUTHOR]

Anthocyanin accumulation is a marked phenotype of plants under environmental stresses. PHYTOCHROME-INTERACTING FACTORs (PIFs) are involved in environment-induced anthocyanin biosynthesis through interacting with the MYB-bHLH-WD40 (MBW) complex. However, the molecular mechanism of this interaction remains unclear. The present study demonstrated that PIF3 and PIF5 can slightly repress anthocyanin accumulation under NaCl, low nitrogen (-N), or 6-BA treatments; in contrast, PIF4 can significantly repress anthocyanin accumulation. Bimolecular fluorescence complementation and yeast two-hybrid assays showed that PIF4 directly interacts with PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1), a MYB transcription factor in the MBW complex. Further analysis revealed that the active phytochrome binding (APB) domain in the N terminus of PIF4 is necessary for the interaction between PIF4 and PAP1. Yeast three-hybrid analysis showed that PIF4 competes with TRANSPARENT TESTA 8 (TT8) to bind PAP1, thereby interfering with the regulation of the MBW protein complex in anthocyanin synthesis. Consistently, the anthocyanin content in pap1-D/35S::PIF4 and 35S::PAP1/35S::PIF4 seedlings was markedly lower than that in pap1-D and 35S::PAP1 under 6-BA, MeJA, –N, and NaCl stresses, implying that overexpression of PIF4 suppresses anthocyanin accumulation in pap1-D and 35S::PAP1. Thus, PIF4 is genetically epistatic to PAP1. Taken together, PIF4 plays a negative role in modulating anthocyanin biosynthesis in Arabidopsis under different stress environments, and PIF4 interacts with PAP1 to affect the integrity of the MBW complex. [ABSTRACT FROM AUTHOR]