UCP1 and AOX1a contribute to regulation of carbon and nitrogen metabolism and yield in Arabidopsis under low nitrogen stress

Effects of OsAOX1a Deficiency on Mitochondrial Metabolism at Critical Node of Seed Viability in Rice

Mitochondrial alternative oxidase 1a (AOX1a) plays an extremely important role in the critical node of seed viability during storage. However, the regulatory mechanism is still poorly understood. The aim of this study was to identify the regulatory mechanisms by comparing OsAOX1a-RNAi and wild-type (WT) rice seed during artificial aging treatment. Weight gain and time for the seed germination percentage decreased to 50% (P50) in OsAOX1a-RNAi rice seed, indicating possible impairment in seed development and storability. Compared to WT seeds at 100%, 90%, 80%, and 70% germination, the NADH- and succinate-dependent O₂ consumption, the activity of mitochondrial malate dehydrogenase, and ATP contents all decreased in the OsAOX1a-RNAi seeds, indicating that mitochondrial status in the OsAOX1a-RNAi seeds after imbibition was weaker than in the WT seeds. In addition, the reduction in the abundance of Complex I subunits showed that the capacity of the mitochondrial electron transfer chain was significantly inhibited in the OsAOX1a-RNAi seeds at the critical node of seed viability. The results indicate that ATP production was impaired in the OsAOX1a-RNAi seeds during aging. Therefore, we conclude that mitochondrial metabolism and alternative pathways were severely inhibited in the OsAOX1a-RNAi seeds at critical node of viability, which could accelerate the collapse of seed viability. The precise regulatory mechanism of the alternative pathway at the critical node of viability needs to be further analyzed. This finding might provide the basis for developing monitoring and warning indicators when seed viability declines to the critical node during storage.

Genome-wide identification of AOX family genes in Moso bamboo and functional analysis of PeAOX1b_2 in drought and salinity stress tolerance

Five PeAOX genes from Moso bamboo genome were identified. PeAOX1b_2-OE improved tolerance to drought and salinity stress in Arabidopsis, indicating it is involved in positive regulation of abiotic stress response. Mitochondrial alternative oxidase (AOX), the important respiratory terminal oxidase in organisms, catalyzes the energy wasteful cyanide (CN)-resistant respiration, which can improve abiotic stresses tolerance and is considered as one of the functional markers for plant resistance breeding. Here, a total of five putative AOX genes (PeAOXs) were identified and characterized in a monocotyledonous woody grass Moso bamboo (Phyllostachys edulis). Phylogenetic analysis revealed that PeAOXs belonged to AOX1 subfamily, and were named PeAOX1a_1, PeAOX1a_2, PeAOX1b_1, PeAOX1b_2 and PeAOX1c, respectively. Evolutionary and divergence patterns analysis revealed that the PeAOX, OsAOX, and BdAOX families experienced positive purifying selection and may have undergone a large-scale duplication event roughly 1.35-155.90 million years ago. Additionally, the organ-specific expression analysis showed that 80% of PeAOX members were mainly expressed in leaf. Promoter sequence analysis of PeAOXs revealed cis-acting regulatory elements (CAREs) responding to abiotic stress. Most PeAOX genes were significantly upregulated after methyl jasmonate (MeJA) and abscisic acid (ABA) treatment. Moreover, under salinity and drought stresses, the ectopic overexpression of PeAOX1b_2 in Arabidopsis enhanced seed germination and seedling establishment, increased the total respiratory rate and the proportion of AOX respiratory pathway in leaf, and enhanced antioxidant ability, suggesting that PeAOX1b_2 is crucial for abiotic stress resistance in Moso bamboo.

The colonization of land was a likely driving force for the evolution of mitochondrial retrograde signalling in plants

Most retrograde signalling research in plants was performed using Arabidopsis, so an evolutionary perspective on mitochondrial retrograde regulation (MRR) is largely missing. Here, we used phylogenetics to track the evolutionary origins of factors involved in plant MRR. In all cases, the gene families can be traced to ancestral green algae or earlier. However, the specific subfamilies containing factors involved in plant MRR in many cases arose during the transition to land. NAC transcription factors with C-terminal transmembrane domains, as observed in the key regulator ANAC017, can first be observed in non-vascular mosses, and close homologs to ANAC017 can be found in seed plants. Cyclin-dependent kinases (CDKs) are common to eukaryotes, but E-type CDKs that control MRR also diverged in conjunction with plant colonization of land. AtWRKY15 can be traced to the earliest land plants, while AtWRKY40 only arose in angiosperms and AtWRKY63 even more recently in Brassicaceae. Apetala 2 (AP2) transcription factors are traceable to algae, but the ABI4 type again only appeared in seed plants. This strongly suggests that the transition to land was a major driver for developing plant MRR pathways, while additional fine-tuning events have appeared in seed plants or later. Finally, we discuss how MRR may have contributed to meeting the specific challenges that early land plants faced during terrestrialization.

Mechanisms Regulating Energy Homeostasis in Plant Cells and Their Potential to Inspire Electrical Microgrids Models

In this paper, the main features of systems that are required to flexibly modulate energy states of plant cells in response to environmental fluctuations are surveyed and summarized. Plant cells possess multiple sources (chloroplasts and mitochondria) to produce energy that is consumed to drive many processes, as well as mechanisms that adequately provide energy to the processes with high priority depending on the conditions. Such energy-providing systems are tightly linked to sensors that monitor the status of the environment and inside the cell. In addition, plants possess the ability to efficiently store and transport energy both at the cell level and at a higher level. Furthermore, these systems can finely tune the various mechanisms of energy homeostasis in plant cells in response to the changes in environment, also assuring the plant survival under adverse environmental conditions. Electrical power systems are prone to the effects of environmental changes as well; furthermore, they are required to be increasingly resilient to the threats of extreme natural events caused, for example, by climate changes, outages, and/or external deliberate attacks. Starting from this consideration, similarities between energy-related processes in plant cells and electrical power grids are identified, and the potential of mechanisms regulating energy homeostasis in plant cells to inspire the definition of new models of flexible and resilient electrical power grids, particularly microgrids, is delineated. The main contribution of this review is surveying energy regulatory mechanisms in detail as a reference and helping readers to find useful information for their work in this research field.