Evolution of cereal floral architecture and threshability.

Hulled grains, while providing natural protection for seeds, pose a challenge to manual threshing due to the pair of glumes tightly encasing them. Based on natural evolution and artificial domestication, gramineous crops evolved various hull-like floral organs. Recently, progress has been made in uncovering novel domesticated genes associated with cereal threshability and deciphering common regulatory modules pertinent to the specification of hull-like floral organs. Here we review morphological similarities, principal regulators, and common mechanisms implicated in the easy-threshing traits of crops. Understanding the shared and unique features in the developmental process of cereal threshability may not only shed light on the convergent evolution of cereals but also facilitate the de novo domestication of wild cereal germplasm resources through genome-editing technologies.

Translation of interacting cavitation bubble in a plane acoustic field.

In a plane acoustic field, a model involving the radial and translational motions of bubble is derived, which is used to numerically investigate the translation of two interacting spherical cavitation bubbles. For the smaller initial distance between bubble centers, we investigate the dynamics of two bubbles, and find that they could come into contact but the velocities of closing to each other are different when the equilibrium radius is different. The results show that when the wavelength of plane acoustic field is much larger than the initial distance, the bubbles are approximately pulsating in phase. Moreover, the velocity of contact process of two bubbles can be changed by adjusting the parameters of plane acoustic field. For increasing in the initial distance, the bubbles would present two translation motions: close to each other for the pulsating in phase and away from each other for the pulsating out of phase, which could be verified by calculating the secondary Bjerknes force. Meanwhile, the larger the initial distance, the smaller the secondary Bjerknes force value is. Understanding the translation of bubble is of great significance for helpful explaining formation of streamer structures in ultrasonic cavitation.

Genetic architecture and molecular regulation of sorghum domestication.

Over time, wild crops have been domesticated by humans, and the knowledge gained from parallel selection and convergent domestication-related studies in cereals has contributed to current techniques used in molecular plant breeding. Sorghum (Sorghum bicolor (L.) Moench) is the world's fifth-most popular cereal crop and was one of the first crops cultivated by ancient farmers. In recent years, genetic and genomic studies have provided a better understanding of sorghum domestication and improvements. Here, we discuss the origin, diversification, and domestication processes of sorghum based on archeological discoveries and genomic analyses. This review also comprehensively summarized the genetic basis of key genes related to sorghum domestication and outlined their molecular mechanisms. It highlights that the absence of a domestication bottleneck in sorghum is the result of both evolution and human selection. Additionally, understanding beneficial alleles and their molecular interactions will allow us to quickly design new varieties by further de novo domestication.

A Gγ protein regulates alkaline sensitivity in crops.

The use of alkaline salt lands for crop production is hindered by a scarcity of knowledge and breeding efforts for plant alkaline tolerance. Through genome association analysis of sorghum, a naturally high-alkaline-tolerant crop, we detected a major locus, Alkaline Tolerance 1 (AT1), specifically related to alkaline-salinity sensitivity. An at1 allele with a carboxyl-terminal truncation increased sensitivity, whereas knockout of AT1 increased tolerance to alkalinity in sorghum, millet, rice, and maize. AT1 encodes an atypical G protein γ subunit that affects the phosphorylation of aquaporins to modulate the distribution of hydrogen peroxide (H2O2). These processes appear to protect plants against oxidative stress by alkali. Designing knockouts of AT1 homologs or selecting its natural nonfunctional alleles could improve crop productivity in sodic lands.

Translation of cavitation bubble near the different walls.

The interaction between spherical cavitation bubble and flat wall is transformed into that between the real bubble and imaging bubble by the method of images. Firstly, we investigate the dynamics of real bubble and matched, inversed or mis-matched imaging bubble driven by a small amplitude ultrasound, revealing the characteristics of the interaction between cavitation bubble and rigid, soft and impedance walls. Then, we emphatically study the dynamics of real bubble and mis-matched imaging bubble driven by a finite amplitude ultrasound, and the interaction characteristics between cavitation bubble and real impedance wall are revealed. The results show that the cavitation bubble is always close to the rigid wall and far away from the soft wall; For the impedance wall, whether the cavitation bubble is far away or close depends on the specific wall parameters. Moreover, the direction and magnitude of bubble's translation velocity can be changed by adjusting the driving parameters. Understanding the interaction between cavitation bubble and impedance wall is of great significance for efficient application of ultrasonic cavitation.

The left-right symmetrical and asymmetrical deformations in a three-bubble system.

This paper studies the simplest system that can possess left-right symmetrical and asymmetrical surroundings, three bubbles in a line. Assuming that the deformations are small, the surfaces of bubbles are described by a combination of the first three Legendre polynomials, that is, spherical symmetrical mode P0, L-R antisymmetrical mode P1, and symmetrical mode P2. A dynamical model is built to describe aspherical oscillations of central and two side bubbles. It is found that when three identical bubbles are separated uniformly, the central bubble only has a P2 component and P1 component tends to zero, while two side bubbles have both P1 and P2 components. When three identical bubbles are separated by different distances, they can be degenerated into a two-bubble system and a free bubble. The bubble deformations contain both P1 and P2 components in the two-bubble system, while both aspherical components P1 and P2 of the free bubble tend to zero. If side bubbles are different in ambient radii but located symmetrically on the left and right of the central bubble, the side bubble pulsated more strongly plays an important role on the deformation of the central one.

Coordinative regulation of ERAD and selective autophagy in plants.

Endoplasmic reticulum-associated degradation (ERAD) plays important roles in plant development, hormone signaling, and plant-environment stress interactions by promoting the clearance of certain proteins or soluble misfolded proteins through the ubiquitin-proteasome system. Selective autophagy is involved in the autophagic degradation of protein aggregates mediated by specific selective autophagy receptors. These two major degradation routes co-operate with each other to relieve the cytotoxicity caused by ER stress. In this review, we analyze ERAD and different types of autophagy, including nonselective macroautophagy and ubiquitin-dependent and ubiquitin-independent selective autophagy in plants, and specifically summarize the selective autophagy receptors characterized in plants. In addition to being a part of selective autophagy, ERAD components also serve as their cargos. Moreover, an ubiquitinated substrate can be delivered to two distinguishable degradation systems, while the underlying determinants remain elusive. These excellent findings suggest an interdependent but complicated relationship between ERAD and selective autophagy. According to this point, we propose several key issues that need to be addressed in the future.

The deubiquitinases UBP12 and UBP13 integrate with the E3 ubiquitin ligase XBAT35.2 to modulate VPS23A stability in ABA signaling.

Ubiquitination-mediated protein degradation in both the 26S proteasome and vacuole is an important process in abscisic acid (ABA) signaling. However, the role of deubiquitination in this process remains elusive. Here, we demonstrate that two deubiquitinating enzymes (DUBs), ubiquitin-specific protease 12 (UBP12) and UBP13, modulate ABA signaling and drought tolerance by deubiquitinating and stabilizing the endosomal sorting complex required for transport-I (ESCRT-I) component vacuolar protein sorting 23A (VPS23A) and thereby affect the stability of ABA receptors in Arabidopsis thaliana. Genetic analysis showed that VPS23A overexpression could rescue the ABA hypersensitive and drought tolerance phenotypes of ubp12-2w or ubp13-1. In addition to the direct regulation of VPS23A, we found that UBP12 and UBP13 also stabilized the E3 ligase XB3 ortholog 5 in A. thaliana (XBAT35.2) in response to ABA treatment. Hence, we demonstrated that UBP12 and UBP13 are previously unidentified rheostatic regulators of ABA signaling and revealed a mechanism by which deubiquitination precisely monitors the XBAT35/VPS23A ubiquitination module in the ABA response.

Pulsation, translation and P1 deformation of two aspherical bubbles in liquid.

In this work, the interactions between the axial translational motions and aspherical oscillations of two gas bubbles in an incompressible liquid are considered. Representing the surface function by the Legendre polynomial of first order, we derive a dynamic model to describe the motions of two aspherical bubbles in Lagrangian mechanics. An apple-shaped bubble from simulations based on the model can be well consistent with known experimental observation. The bubble appears as the shape of a sphere at maximum expansion. The maximum asymmetry of the bubbles occurs during collapse. The surface tension is a key factor to stable oscillatory deformation. It is also found that the aspherical amplitudes of two bubbles decrease with increasing distance or decreasing driving pressure.

Natural variation in Glume Coverage 1 causes naked grains in sorghum.

One of the most critical steps in cereal threshing is the ease with which seeds are detached from sticky glumes. Naked grains with low glume coverage have dramatically increased threshing efficiency and seed quality. Here, we demonstrate that GC1 (Glume Coverage 1), encoding an atypical G protein γ subunit, negatively regulates sorghum glume coverage. Naturally truncated variations of GC1 C-terminus accumulate at higher protein levels and affect the stability of a patatin-related phospholipase SbpPLAII-1. A strong positive selection signature around the GC1 genic region is found in the naked sorghum cultivars. Our findings reveal a crucial event during sorghum domestication through a subtle regulation of glume development by GC1 C-terminus variation, and establish a strategy for future breeding of naked grains.

Creation of fragrant sorghum by CRISPR/Cas9.

Sorghum, the fifth largest cereal crop, has high value as a staple food and raw material for liquor and vinegar brewing. Due to its high biomass and quality, it is also used as the second most planted silage resource. No fragrant sorghums are currently on the market. Through CRISPR/Cas9-mediated knockout of SbBADH2, we obtained sorghum lines with extraordinary aromatic smell in both seeds and leaves. Animal feeding experiments showed that fragrant sorghum leaves were attractable. We believe this advantage will produce great value in the sorghum market for both grain and whole biomass forage.

Comparative Transcriptome Analysis of Two Sweet Sorghum Genotypes with Different Salt Tolerance Abilities to Reveal the Mechanism of Salt Tolerance.

Sweet sorghum is a C4 crop that can be grown for silage forage, fiber, syrup and fuel production. It is generally considered a salt-tolerant plant. However, the salt tolerance ability varies among genotypes, and the mechanism is not well known. To further uncover the salt tolerance mechanism, we performed comparative transcriptome analysis with RNA samples in two sweet sorghum genotypes showing different salt tolerance abilities (salt-tolerant line RIO and salt-sensitive line SN005) upon salt treatment. These response processes mainly focused on secondary metabolism, hormone signaling and stress response. The expression pattern cluster analysis showed that RIO-specific response genes were significantly enriched in the categories related to secondary metabolic pathways. GO enrichment analysis indicated that RIO responded earlier than SN005 in the 2 h after treatment. In addition, we identified more transcription factors (TFs) in RIO than SN005 that were specifically expressed differently in the first 2 h of salt treatment, and the pattern of TF change was obviously different. These results indicate that an early response in secondary metabolism might be essential for salt tolerance in sweet sorghum. In conclusion, we found that an early response, especially in secondary metabolism and hormone signaling, might be essential for salt tolerance in sweet sorghum.

The dynamics of cavitation bubbles in a sealed vessel.

A model of cavitation bubbles is derived in liquid confined in an elastic sealed vessel driven by ultrasound. In this model, an assumption that the pressure acting on the sealed vessel due to bubble pulsations is proportional to total volume change of bubbles is made. Numerical simulations are carried out for a single bubble and for bubbles. The results show that the pulsation of a single bubble can be suppressed to a large extent in sealed vessel, and that of two matched bubbles with same ambient radius can be further suppressed. However, when two mismatched bubbles have the same ambient radii, an interesting breathing phenomenon takes place, where one bubble pulsates inversely with the other one. Due to this breathing phenomenon the suppression effect becomes weak, so the maximum radii of two mismatched bubbles can be larger than that of a single bubble or that of two matched bubbles in sealed vessel. Besides that, for two mismatched bubbles with different ambient radii, the small one in sealed vessel under some certain parameters can pulsate as strong as or even stronger than that of a single bubble in an open vessel.

Endoplasmic reticulum-related E3 ubiquitin ligases: Key regulators of plant growth and stress responses.

Accumulating evidence has revealed that the ubiquitin proteasome system plays fundamental roles in the regulation of diverse cellular activities in eukaryotes. The ubiquitin protein ligases (E3s) are central to the proteasome system because of their ability to determine its substrate specificity. Several studies have demonstrated the essential role of a group of ER (endoplasmic reticulum)-localized E3s in the positive or negative regulation of cell homeostasis. Most ER-related E3s are conserved between plants and mammals, and a few plant-specific components have been reported. In this review, we summarize the functions of ER-related E3s in plant growth, ER-associated protein degradation and ER-phagy, abiotic and biotic stress responses, and hormone signaling. Furthermore, we highlight several questions that remain to be addressed and suggest directions for further research on ER-related E3 ubiquitin ligases.

ZmbHLH124 identified in maize recombinant inbred lines contributes to drought tolerance in crops.

Due to climate change, drought has become a severe abiotic stress that affects the global production of all crops. Elucidation of the complex physiological mechanisms underlying drought tolerance in crops will support the cultivation of new drought-tolerant crop varieties. Here, two drought-tolerant lines, RIL70 and RIL73, and two drought-sensitive lines, RIL44 and RIL93, from recombinant inbred lines (RIL) generated from maize drought-tolerant line PH4CV and drought-sensitive line F9721, were selected for a comparative RNA-seq study. Through transcriptome analyses, we found that gene expression differences existed between drought-tolerant and -sensitive lines, but also differences between the drought-tolerant lines, RIL70 and RIL73. ZmbHLH124 in RIL73, named as ZmbHLH124T-ORG which origins from PH4CV and encodes a bHLH type transcription factor, was specifically up-regulated during drought stress. In addition, we identified a substitution in ZmbHLH124 that produced an early stop codon in sensitive lines (ZmbHLH124S-ORG ). Overexpression of ZmbHLH124T-ORG , but not ZmbHLH124S-ORG , in maize and rice enhanced plant drought tolerance and up-regulated the expression of drought-responsive genes. Moreover, we found that ZmbHLH124T-ORG could directly bind the cis-acting elements in ZmDREB2A promoter to enhance its expression. Taken together, this work identified a valuable genetic locus and provided a new strategy for breeding drought-tolerant crops.

ERAD-related E2 and E3 enzymes modulate the drought response by regulating the stability of PIP2 aquaporins.

Endoplasmic reticulum-associated degradation (ERAD) is known to regulate plant responses to diverse stresses, yet its underlying molecular mechanisms and links to various stress signaling pathways are poorly understood. Here, we show that the ERAD component ubiquitin-conjugating enzyme UBC32 positively regulates drought tolerance in Arabidopsis thaliana by targeting the aquaporins PIP2;1 and PIP2;2 for degradation. Furthermore, we demonstrate that the RING-type ligase Rma1 acts together with UBC32 and that the E2 activity of UBC32 is essential for the ubiquitination of Rma1. This complex ubiquitinates a phosphorylated form of PIP2;1 at Lys276 to promote its degradation, thereby enhancing plant drought tolerance. Extending these molecular insights into crops, we show that overexpression of Arabidopsis UBC32 also improves drought tolerance in rice (Oryza sativa). Thus, beyond uncovering the molecular basis of an ERAD-regulated stress response, our study suggests multiple potential strategies for engineering crops with improved drought tolerance.

The role of the bubble-bubble interaction on radial pulsations of bubbles.

Using a model that with or without considering the interaction between bubbles through the radiated pressure waves, numerical simulations of cavitation bubbles have been performed in order to study the effect of the bubble-bubble interaction on radial pulsations of bubbles. Comparing the results obtained by with or without considering the bubble-bubble interaction, it is suggested that the suppression or enlargement property of expansion ratios of bubbles due to the bubble-bubble interaction largely depends on the ultrasound parameters, the ambient bubble radii, the distances between bubbles and the number of bubbles (in multi-bubble environment, the last two aspects can be expressed using the coupling strength). The frequency response curve of expansion ratio decreases and shifts to left due to the bubble-bubble interaction and the larger the coupling strength is, the more the left-shifting is.

The UBC27-AIRP3 ubiquitination complex modulates ABA signaling by promoting the degradation of ABI1 in Arabidopsis.

Abscisic acid (ABA) is the key phytohormone in plant drought tolerance and stress adaptation. The clade A protein phosphatase 2Cs (PP2Cs) like ABI1 (ABA-INSENSITIVE 1) work as coreceptors of ABA and regulate multiple ABA responses. Ubiquitination of ABI1 has been proven to play important regulatory roles in ABA signaling. However, the specific ubiquitin conjugating enzyme (E2) involved is unknown. Here, we report that UBC27 is an active E2 that positively regulates ABA signaling and drought tolerance. UBC27 forms the E2-E3 pair with the drought regulator RING E3 ligase AIRP3. Both UBC27 and AIRP3 interact with ABI1 and affect the ubiquitination and degradation of ABI1. ABA activates the expression of UBC27, inhibits the proteasome degradation of UBC27, and enhances the interaction between UBC27 and ABI1 to increase its activity. These findings uncover a regulatory mechanism in ABA signaling and drought response and provide a further understanding of the plant ubiquitination system and ABA signaling pathway.

ESCRT-I Component VPS23A Sustains Salt Tolerance by Strengthening the SOS Module in Arabidopsis.

The Salt-Overly-Sensitive (SOS) signaling module, comprising the sodium-transport protein SOS1 and the regulatory proteins SOS2 and SOS3, is well known as the central salt excretion system, which helps protect plants against salt stress. Here we report that VPS23A, a component of the ESCRT (endosomal sorting complex required for transport), plays an essential role in the function of the SOS module in conferring plant salt tolerance. VPS23A enhances the interaction of SOS2 and SOS3. In the presence of salt stress, VPS23A positively regulates the redistribution of SOS2 to the plasma membrane, which then activates the antiporter activity of SOS1 to reduce Na+ accumulation in plant cells. Genetic evidence demonstrated that plant salt tolerance achieved by the overexpression of SOS2 and SOS3 dependeds on VPS23A. Taken together, our results revealed that VPS23A is a crucial regulator of the SOS module and affects the localization of SOS2 to the cell membrane. Moreover, the strong salt tolerance of Arabidopsis seedlings conferred by the engineered membrane-bound SOS2 revealed the significance of SOS2 sorting to the cell membrane in achieving its function, providing a potential strategy for crop salt tolerance engineering.

Control of Bird Feeding Behavior by Tannin1 through Modulating the Biosynthesis of Polyphenols and Fatty Acid-Derived Volatiles in Sorghum.

Bird predation during seed maturation causes great loss to agricultural production. In this study, through GWAS analysis of a large-scale sorghum germplasm diversity panel, we identified that Tannin1, which encodes a WD40 protein functioning in the WD40/MYB/bHLH complex, controls bird feeding behavior in sorghum. Metabolic profiling analysis showed that a group of sorghum accessions preferred by birds contain mutated tan1-a/b alleles and accumulate significantly lower levels of anthocyanins and condensed tannin compounds. In contrast, a variety of aromatic and fatty acid-derived volatiles accumulate at significantly higher levels in these bird-preference accessions. We subsequently conducted both sparrow feeding and sparrow volatile attractant assays, which confirmed, respectively, the antifeedant and attractant functions of these differentially accumulated metabolites. In addition, the connection between the biosynthesis pathway of anthocyanin and proanthocyanidin and the pathway of fatty acid-derived volatile biosynthesis was demonstrated by discovering that Tannin1 complex modulates fatty acid biosynthesis by regulating the expression of SbGL2 in sorghum, thus affecting the accumulation of fatty acid-derived volatiles. Taken together, our study identified Tannin1 as the gene underlying the major locus controlling bird feeding behavior in sorghum, illustrating an example of the identification of an ecologically impactful molecular mechanism from field observation and providing significant insights into the chemistry of bird-plant ecological interactions.