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Abstract Different intensities of high temperatures affect the growth of photosynthetic cells in nature. To elucidate the underlying mechanisms, we cultivated the unicellular green alga Chlamydomonas reinhardtii under highly controlled photobioreactor conditions and revealed systems-wide shared and unique responses to 24-hour moderate (35°C) and acute (40°C) high temperatures and subsequent recovery at 25°C. We identified previously overlooked unique elements in response to moderate high temperature. Heat at 35°C transiently arrested the cell cycle followed by partial synchronization, up-regulated transcripts/proteins involved in gluconeogenesis/glyoxylate-cycle for carbon uptake and promoted growth. But 40°C disrupted cell division and growth. Both high temperatures induced photoprotection, while 40°C distorted thylakoid/pyrenoid ultrastructure, affected the carbon concentrating mechanism, and decreased photosynthetic efficiency. We demonstrated increased transcript/protein correlation during both heat treatments and hypothesize reduced post-transcriptional regulation during heat may help efficiently coordinate thermotolerance mechanisms. During recovery after both heat treatments, especially 40°C, transcripts/proteins related to DNA synthesis increased while those involved in photosynthetic light reactions decreased. We propose down-regulating photosynthetic light reactions during DNA replication benefits cell cycle resumption by reducing ROS production. Our results provide potential targets to increase thermotolerance in algae and crops. 

The unicellular green alga Chlamydomonas reinhardtii is an excellent model organism to investigate many essential cellular processes in photosynthetic eukaryotes. Two commonly used background strains of Chlamydomonas are CC-1690 and CC-5325. CC-1690, also called 21gr, has been used for the Chlamydomonas genome project and several transcriptome analyses. CC-5325 is the background strain for the Chlamydomonas Library Project (CLiP). Photosynthetic performance in CC-5325 has not been evaluated in comparison with CC-1690. Additionally, CC-5325 is often considered to be cell-wall deficient, although detailed analysis is missing. The circadian rhythms in CC-5325 are also unclear. To fill these knowledge gaps and facilitate the use of the CLiP mutant library for various screens, we performed phenotypic comparisons between CC-1690 and CC-5325. Our results showed that CC-5325 grew faster heterotrophically in dark and equally well in mixotrophic liquid medium as compared to CC-1690. CC-5325 had lower photosynthetic efficiency and was more heat-sensitive than CC-1690. Furthermore, CC-5325 had an intact cell wall which had comparable integrity to that in CC-1690 but appeared to have reduced thickness. Additionally, CC-5325 could perform phototaxis, but could not maintain a sustained circadian rhythm of phototaxis as CC1690 did. Finally, in comparison to CC-1690, CC-5325 had longer cilia in the medium with acetate but slower swimming speed in the medium without nitrogen and acetate. Our results will be useful for researchers in the Chlamydomonas community to choose suitable background strains for mutant analysis and employ the CLiP mutant library for genome-wide mutant screens under appropriate conditions, especially in the areas of photosynthesis, thermotolerance, cell wall, and circadian rhythms.

 

The ruminants are one of the most successful mammalian lineages, exhibiting morphological and habitat diversity and containing several key livestock species. To better understand their evolution, we generated and analyzed de novo assembled genomes of 44 ruminant species, representing all six Ruminantia families. We used these genomes to create a time-calibrated phylogeny to resolve topological controversies, overcoming the challenges of incomplete lineage sorting. Population dynamic analyses show that population declines commenced between 100,000 and 50,000 years ago, which is concomitant with expansion in human populations. We also reveal genes and regulatory elements that possibly contribute to the evolution of the digestive system, cranial appendages, immune system, metabolism, body size, cursorial locomotion, and dentition of the ruminants. 

Plastid evolution has been attributed to a single primary endosymbiotic event that occurred about 1.6 billion years ago (BYA) in which a cyanobacterium was engulfed and retained by a eukaryotic cell, although early steps in plastid integration are poorly understood. The photosynthetic amoebaPaulinella chromatophorarepresents a unique model for the study of plastid evolution because it contains cyanobacterium‐derived photosynthetic organelles termed ‘chromatophores’ that originated relatively recently (0.09–0.14 BYA). The chromatophore genome is about a third the size of the genome of closely related cyanobacteria, but 10‐fold larger than most plastid genomes. Several genes have been transferred from the chromatophore genome to the host nuclear genome through endosymbiotic gene transfer (EGT). Some EGT‐derived proteins could be imported into chromatophores for function. Two photosynthesis‐related genes (psaI and csos4A) are encoded by both the nuclear and chromatophore genomes, suggesting that EGT inPaulinella chromatophorais ongoing. Many EGT‐derived genes encode proteins that function in photosynthesis and photoprotection, including an expanded family of high‐light‐inducible (ncHLI) proteins. Cyanobacterialhligenes are high‐light induced and required for cell viability under excess light. We examined the impact of light onPaulinella chromatophoraand found that this organism is light sensitive and lacks light‐induced transcriptional regulation of chromatophore genes and most EGT‐derived nuclear genes. However, several ncHLIgenes have reestablished light‐dependent regulation, which appears analogous to what is observed in cyanobacteria. We postulate that expansion of the ncHLIgene family and its regulation may reflect the light/oxidative stress experienced byPaulinella chromatophoraas a consequence of the as yet incomplete integration of host and chromatophore metabolisms.

 

Cloud servers provide cloud users with storage service and allow cloud users to access their files anytime. To guarantee security of the stored files, auditors need to periodically verify data block correctness. In the existing integrity verification schemes, there are few protocols to support the users' identity anonymity and the data block dynamic operation simultaneously. In this paper, we present an efficient and anonymous identity‐based integrity auditing protocol, which supports data dynamic operation and can be extended to support batch auditing in the multifile or multiuser setting. Our scheme not only resists forgery, replace, and replay attacks but also maintains users' anonymity, which is not discussed in other related techniques. The computation efficiency of auditor is improved a lot. Comparing with Zhang's efficient identity‐based public auditing scheme, our scheme is more suitable for actual application scenario with large‐scale storage system.