The photosynthetic CO 2 -fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) is inhibited by nonproductive binding of its substrate ribulose-1,5-bisphosphate (RuBP) and other sugar phosphates. Reactivation requires ATP-hydrolysis-powered remodeling of the inhibited complexes by diverse molecular chaperones known as rubisco activases (Rcas). Eukaryotic phytoplankton of the red plastid lineage contain so-called red-type rubiscos, some of which have been shown to possess superior kinetic properties to green-type rubiscos found in higher plants. These organisms are known to encode multiple homologs of CbbX, the α-proteobacterial red-type activase. Here we show that the gene products of two cbbX genes encoded by the nuclear and plastid genomes of the red algae Cyanidioschyzon merolae are nonfunctional in isolation, but together form a thermostable heterooligomeric Rca that can use both α-proteobacterial and red algal-inhibited rubisco complexes as a substrate. The mechanism of rubisco activation appears conserved between the bacterial and the algal systems and involves threading of the rubisco large subunit C terminus. Whereas binding of the allosteric regulator RuBP induces oligomeric transitions to the bacterial activase, it merely enhances the kinetics of ATP hydrolysis in the algal enzyme. Mutational analysis of nuclear and plastid isoforms demonstrates strong coordination between the subunits and implicates the nuclearencoded subunit as being functionally dominant. The plastid-encoded subunit may be catalytically inert. Efforts to enhance crop photosynthesis by transplanting red algal rubiscos with enhanced kinetics will need to take into account the requirement for a compatible Rca.rubisco | activase | photosynthesis | AAA + proteins | red algae

Over 70 years ago, increased spontaneous mutation rates were observed in Drosophila spp. hybrids, but the genetic basis of this phenomenon is not well understood. The model plant Arabidopsis (Arabidopsis thaliana) offers unique opportunities to study the types of mutations induced upon hybridization and the frequency of their occurrence. Understanding the mutational effects of hybridization is important, as many crop plants are grown as hybrids. Besides, hybridization is important for speciation and its effects on genome integrity could be critical, as chromosomal rearrangements can lead to reproductive isolation. We examined the rates of hybridizationinduced point and frameshift mutations as well as homologous recombination events in intraspecific Arabidopsis hybrids using a set of transgenic mutation detector lines that carry mutated or truncated versions of a reporter gene. We found that hybridization alters the frequency of different kinds of mutations. In general, Columbia (Col) 3 Cape Verde Islands and Col 3 C24 hybrid progeny had decreased T→G and T→A transversion rates but an increased C→T transition rate. Significant changes in frameshift mutation rates were also observed in some hybrids. In Col 3 C24 hybrids, there is a trend for increased homologous recombination rates, except for the hybrids from one line, while in Col 3 Cape Verde Islands hybrids, this rate is decreased. The overall genetic distance of the parents had no influence on mutation rates in the progeny, as closely related accessions on occasion displayed higher mutation rates than accessions that are separated farther apart. However, reciprocal hybrids had significantly different mutation rates, suggesting parentof-origin-dependent effects on the mutation frequency.In plants, somatic mutations are an important source of genetic variability, which can, in principle, be passed on as heritable changes to the progeny of an individual (Baake and Gabriel, 1999). Plants have higher point mutation rates than animals (Kovalchuk et al., 2000) and do not have a fixed germline, such that there is a chance for somatic mutations to be transmitted to the next generation (Walbot and Evans, 2003). In contrast, animals cannot transmit somatic mutations to their progeny, as their germline cells are set aside early during development.Mutation rates have been estimated in several organisms, including bacteria and mammals (Kovalchuk et al., 2000). The easiest phenotype for estimating mutation rates in plants is chlorophyll deficiency or albinism. In barley (Hordeum vulgare), it was estimated that albino phenotypes can result from mutations in about 300 different nuclear genes (Klekowski, 1992). Mutations leading to chlorophyll deficiency in barley and buckwheat (Fagopyrum esculentum) occur at rates of 3.2 3 10 24 and 3.1 3 10 24 events per nuclear genome per generation, respectively. In long-lived red mangrove (Rhizophora mangle) plants, this rate was found to be 25 times higher, which led to the prediction that long-lived plants have higher mutation rates per...

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Given the current coronavirus (COVID-19) situation around the world, we may have to face a long-term battle with coronavirus. It is necessary to prepare and stay resilient with some other techniques to improve air quality in buildings, especially in clinics and hospitals. In this paper, we have developed Ultraviolet-C (UVC) light-emitting diode (LED) modules which can be implemented in air ducts in heating, ventilation, and air conditioning system for airborne disinfection. An LED module is designed with LED panels as the basic unit so that it is easy to scale up to accommodate for air ducts with different sizes. Both experiments and simulations are carried out to study its disinfection performance. The results show that more than 76% and 85% of the pathogen can be inactivated within 60 and 90 min, respectively, in a meeting room with a volume of 107 m3 by using one LED module. Simulations for two LED modules show that the disinfection efficacy is more than two times compared to that of one LED module. In addition to the pathogen used in the experiments, the disinfection performance of the LED module for inactivation of SARS-CoV-2 virus based on the literature is investigated numerically. It shows that more than 99.70% of pathogens receive UV dose larger than 4.47 J/m2, leading to an almost 89.10% disinfection rate for SARS-CoV-2 virus within one hour using the two LED modules in the same meeting room.

2PG 2-phosphoglycolate 3PG 3-phosphoglycerate 4-hb 4-helix bundle subdomain 8102Rca Rubisco activase of Synechococcus sp. WH8102 AAA+ ATPase associated with various cellular activities ADP Adenosine diphosphate ATP Adenosine 5'-triphosphate b6f Cytochrome b6f complex C tail Red-type Rubisco large subunits's C terminal extension CA1P 2-carboxy-D-arabinitoll-phosphate CABP 2-carboxyarabinitol-1,5-bisphosphate CBB Calvin-Benson-Bassham cfxQ Alternative name for CbbX Cm, C. merolae Cyanidioschyzon merolae

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