Spatiotemporal Production of Reactive Oxygen Species by NADPH Oxidase Is Critical for Tapetal Programmed Cell Death and Pollen Development in Arabidopsis

HSP70 and APX1 play important roles in cotton male fertility by mediating ROS homeostasis

Male sterility is used in the production of hybrid seeds and can improve the breeding efficiency of cotton hybrids. Reactive oxygen species is closely associated with the tapetum and pollen development, but their relationship in cotton male fertility remains unclear. In this study, we comprehensively compared the cytology and proteome of the anthers from an Upland cotton (Gossypium hirsutum) material, Shida 98 (WT), and its nearly-isogenic male sterile line Shida 98A (MS). Cytology indicated delayed PCD in the tapetum and defects in microspores in MS anthers. And further studies revealed disruption of ROS homeostasis. Proteomic analysis identified proteins with differential abundance mainly being related to redox homeostasis, protein folding, and apoptotic signaling pathways. GhAPX1 interacted with GhHSP70 and played a crucial role in the development of cotton anthers. Exogenous application of HSP70 inhibitor increased H2O2 content and decreased the activity of APX1 and pollen viability. The GhAPX1 mutants generated by CRISPR/Cas9-mediated gene editing exhibited premature degradation of the tapetum, significant decrease in pollen viability, and significant increase in H2O2 content. Altogether, our results imply HSP70 and APX1 being the key players jointly regulating male fertility by mediating ROS homeostasis. These results provide insights into the proteins associated with male fertility.

The transcription factor LBD10 sustains pollen tube growth and integrity by modulating reactive oxygen species homeostasis via the regulation of flavonol biosynthesis in Arabidopsis

Reproduction in angiosperms relies on the precise growth of pollen tubes, facilitating the delivery of sperm cells to the ovule for double fertilization. LATERAL ORGAN BOUNDARIES DOMAIN10 (LBD10), a plant-specific transcription factor, plays a pivotal role in Arabidopsis pollen development. Here, we uncovered LBD10's function in sustaining pollen tube growth and integrity. The lbd10 mutant exhibited elevated levels of reactive oxygen species (ROS) and hydrogen peroxide (H2O2) in both pollen grains and tubes, leading to compromised pollen tube growth. The inhibition of ROS synthesis and scavenging of excess ROS with an antioxidant treatment each alleviated these defects in lbd10. The lbd10 mutant displayed reduced flavonol accumulation in both pollen grains and tubes. All the altered phenotypes of lbd10 were complemented by expressing LBD10 under its native promoter. Exogenous application of flavonoids recused the defects in pollen tube growth and integrity in lbd10, along with reducing the excess levels of ROS and H2O2. LBD10 directly binds the promoters of key flavonol biosynthesis genes in chromatin and promotes reporter gene expression in Arabidopsis mesophyll protoplasts. Our findings indicate that LBD10 modulates ROS homeostasis by transcriptionally activating genes crucial for flavonol biosynthesis, thereby maintaining pollen tube growth and integrity.

Molecular mechanisms underlying the negative effects of transient heatwaves on crop fertility

Transient heatwaves occurring more frequently as the climate warms, yet their impacts on crop yield are severely underestimated and even overlooked. Heatwaves lasting only a few days or even hours during sensitive stages, such as microgametogenesis and flowering, can significantly reduce crop yield by disrupting plant reproduction. Recent advances in multi-omics and GWAS analysis have shed light on the specific organs (e.g., pollen, lodicule, style), key metabolic pathways (sugar and reactive oxygen species metabolism, Ca2+ homeostasis), and essential genes that are involved in crop responses to transient heatwaves during sensitive stages. This review therefore places particular emphasis on heat-sensitive stages, with pollen development, floret opening, pollination, and fertilization as the central narrative thread. The multifaceted effects of transient heatwaves and their molecular basis are systematically reviewed, with a focus on key structures such as the lodicule and tapetum. A number of heat-tolerance genes associated with these processes have been identified in major crops like maize and rice. The mechanisms and key heat-tolerance genes shared among different stages may facilitate the more precise improvement of heat-tolerant crops.

Overexpression of OsRbohH Enhances Heat and Drought Tolerance through ROS Homeostasis and ABA Mediated Pathways in Rice (Oryza sativa L.)

Respiratory burst oxidase homologs (Rbohs) are the primary producers of reactive oxygen species (ROS), which have been demonstrated to play critical roles in plant responses to abiotic stress. Here, we explored the function of OsRbohH in heat and drought stress tolerance by generating overexpression lines (OsRbohH-OE). OsRbohH was highly induced by various abiotic stress and hormone treatments. Compared to wild-type (WT) controls, OsRbohH-OE plants exhibited enhanced tolerance to heat and drought, as determined by survival rate analyses and total chlorophyll content. Histochemical staining revealed that OsRbohH-OE accumulated less ROS. This is consistent with the observed increase in catalase (CAT) and peroxidase (POD) activities, as well as a reduced electrolyte leakage rate and malondialdehyde (MDA) content. Moreover, OsRbohH-OE exhibited enhanced sensitivity to exogenous abscisic acid (ABA), accompanied by altered expression levels of ABA synthesis and catabolic genes. Further analysis indicated that transgenic lines had lower transcripts of ABA signaling-related genes (OsDREB2A, OsLEA3, OsbZIP66, and OsbZIP72) under heat but higher levels under drought than WT. In conclusion, these results suggest that OsRbohH is a positive regulator of heat and drought tolerance in rice, which is probably performed through OsRbohH-mediated ROS homeostasis and ABA signaling.

Temperature change regulates pollen fertility of a PTGMS rice line PA64S by modulating the ROS homeostasis and PCD within the tapetum

Photoperiod and temperature-sensitive male sterility rice is an important line for two-line hybrid rice, and the changes in the cultivation temperature strictly control its pollen fertility. However, the mechanism by which temperature variation regulates pollen fertility is still unclear. This study obtained stable fertile PA64S(F) and sterile PA64S(S) rice from PA64S by controlling temperature changes. PA64S(F) shows a normal anther development and fertile pollen under low temperature (21°C), and PA64S(S) shows delayed degradation of the tapetum cells, leading to abnormal pollen wall formation and ubisch development under normal temperature (28°C). The accumulation of reactive oxygen species (ROS) positively correlates with the programmed cell death (PCD) process of tapetum cells. The delayed accumulation of ROS in the PA64S(S) tapetum at early stages leads to a delayed initiation of the PCD process. Importantly, we localized ascorbic acid (ASA) accumulation in the tapetum cells and determined that ASA is a major antioxidant for ROS homeostasis. ROS-inhibited accumulation plants (PA64S-ASA) demonstrated pollen sterility, higher ASA and lower ROS accumulation in the tapetum, and the absence of PCD processes in the tapetum cell. Abnormal changes in the tapetum of PA64S(S) rice disrupted metabolic pathways such as lipid metabolism, cutin and wax synthesis, sugar accumulation, and phenylpropane, affecting pollen wall formation and substance accumulation, suggesting that the timely accumulation of ROS is critical for male fertility. This study highlights the central role of ROS homeostasis in fertility alteration and also provides an avenue to address the effect of environmental temperature changes on pollen fertility in rice.

The Brassica napus phytoglobin 1 (BnPgb1) mitigates the decrease in plant fertility resulting from high temperature stress

High temperature stress during flowering adversely affects plant fertility, decreasing plant productivity. Daily cycles of heat stress (HS), imposed on Brassica napus L. plants by slowly ramping the temperature from 23 °C to 35 °C before lowering back to pre-stress conditions, inhibited flower and silique formation, with fewer seeds per silique during the stress period, as well as decreased pollen viability. Heat stress also elevated the transcripts and protein levels of class 1 phytoglobin BnPgb1, with the protein accumulating preferentially within the anther walls. Over-expression of BnPgb1 was sufficient to attenuate the reduction in plant fertility at high temperatures while its down-regulation exacerbated the effects of HS. Relative to WT anthers, the rise in ROS and ROS-induced damage caused by HS was limited when BnPgb1 was over-expressed, and this was linked to changes in antioxidant responses. High temperatures reduced the level of ascorbic acid (AsA) in anthers by favoring its oxidation via ascorbate oxidase (AOA) and limiting its regeneration through suppression of monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR). Anthers of heat-stressed plants over-expressing BnPgb1 retained a higher AsA content with concomitant increased activities of DHAR, MDHAR, ascorbate peroxidase (APX) and superoxide dismutase (SOD). These changes suggest that BnPgb1 potentiates antioxidant responses during HS which mitigate the depression of fertility.

Pollen viability, longevity, and function in angiosperms: key drivers and prospects for improvement

Pollen grains are central to sexual plant reproduction and their viability and longevity/storage are critical for plant physiology, ecology, plant breeding, and many plant product industries. Our goal is to present progress in assessing pollen viability/longevity along with recent advances in our understanding of the intrinsic and environmental factors that determine pollen performance: the capacity of the pollen grain to be stored, germinate, produce a pollen tube, and fertilize the ovule. We review current methods to measure pollen viability, with an eye toward advancing basic research and biotechnological applications. Importantly, we review recent advances in our understanding of how basic aspects of pollen/stigma development, pollen molecular composition, and intra- and intercellular signaling systems interact with the environment to determine pollen performance. Our goal is to point to key questions for future research, especially given that climate change will directly impact pollen viability/longevity. We find that the viability and longevity of pollen are highly sensitive to environmental conditions that affect complex interactions between maternal and paternal tissues and internal pollen physiological events. As pollen viability and longevity are critical factors for food security and adaptation to climate change, we highlight the need to develop further basic research for better understanding the complex molecular mechanisms that modulate pollen viability and applied research on developing new methods to maintain or improve pollen viability and longevity.

Cell death in bryophytes: emerging models to study core regulatory modules and conserved pathways

This review summarizes recent progress in our current understanding of the mechanisms underlying the cell death pathways in bryophytes, focusing on conserved pathways and particularities in comparison to angiosperms. Regulated cell death (RCD) plays key roles during essential processes along the plant life cycle. It is part of specific developmental programmes and maintains homeostasis of the organism in response to unfavourable environments. Bryophytes could provide valuable models to study developmental RCD processes as well as those triggered by biotic and abiotic stresses. Some pathways analogous to those present in angiosperms occur in the gametophytic haploid generation of bryophytes, allowing direct genetic studies. In this review, we focus on such RCD programmes, identifying core conserved mechanisms and raising new key questions to analyse RCD from an evolutionary perspective.

ldi-miR396-LdPMaT1 enhances reactive oxygen species scavenging capacity and promotes drought tolerance in Lilium distichum Nakai autotetraploids

Drought is a key environmental stress that inhibits plant growth, development, yield and quality. Whole-genome replication is an effective method for breeding drought resistant cultivars. Here, we evaluated the tolerance of Lilium distichum Nakai diploids (2n = 2× = 24) and artificially induced autotetraploids (2n = 4× = 48) to drought simulated by polyethylene glycol (PEG) stress. Autotetraploids showed stronger drought tolerance than diploids, and high-throughput sequencing during PEG stress identified five differentially expressed miRNAs. Transcriptome analysis revealed significantly different reactive oxygen species (ROS)-scavenger expression levels between diploids and autotetraploids, which increased the drought tolerance of autotetraploids. Specifically, we identified ldi-miR396b and its only target gene (LdPMaT1) for further study based on its expression level and ROS-scavenging ability in response to drought stress (DS). Autotetraploids showed higher expression of LdPMaT1 and significantly downregulated expression of ldi-miR396b under DS compared with diploids. Through a short tandem target mimic (STTM) in transgenic lilies, functional studies revealed that miR396b silencing promotes LdPMaT1 expression and the DS response. Under PEG stress, STTM393 transgenic lines showed improved drought resistance mediated by lowered MDA content but exhibited high antioxidant enzyme activity, consistent with the autotetraploid results. Collectively, these findings suggest that ldi-miR396b-LdPMaT1 potentially enhances ROS-scavenging ability, which contributes to improved stress adaptation in autotetraploid lilies.

The chloroplast singlet oxygen-triggered biosynthesis of salicylic acid and jasmonic acid is mediated by EX1 and GUN1 in Arabidopsis

Reactive oxygen species (ROS) and defence hormones like salicylic acid (SA) and jasmonic acid (JA) play pivotal roles in triggering cell death. However, the precise mechanism governing the interaction between ROS and SA/JA remains elusive. Recently, our research revealed that RNAi mutants with suppressed expression of PROGRAMMED CELL DEATH8 (PCD8) exhibit an overabundance of tetrapyrrole intermediates, particularly uroporphyrinogen III (Uro III), leading to the accumulation of singlet oxygen (1O2) during the transition from darkness to light, thereby instigating leaf necrosis. In this investigation, we uncovered that 1O2 stimulates biosynthesis of SA and JA, activating SA/JA signalling and the expression of responsive genes in PCD8 RNAi (pcd8) mutants. Introducing NahG or knocking out PAD4 or NPR1 significantly alleviates the cell death phenotype of pcd8 mutants, while coi1 partially mitigates the pcd8 phenotype. Further exploration revealed that EX1 and GUN1 can partially rescue the pcd8 phenotype by reducing the levels of Uro III and 1O2. Notably, mutations in EX1 mutations but not GUN1, substantially diminish SA content in pcd8 mutants compared to the wild type, implying that EX1 acts as the primary mediator of 1O2 signalling-mediated SA biosynthesis. Moreover, the triple ex1 gun1 pcd8 displays a phenotype similar to ex1. Overall, our findings underscore that the 1O2-induced cell death phenotype requires EX1/GUN1-mediated retrograde signalling in pcd8 mutants, providing novel insights into the interplay between ROS and SA/JA.

Heat-stress-induced ROS in maize silks cause late pollen tube growth arrest and sterility

The reproductive phase of plants is highly sensitive to ambient temperature stresses. To investigate sensitivity of female reproductive organs in grass crops during the pollination phase, we exposed the elongated stigma (silk) of maize to ambient environment at the silking stage. Moderate heat stress causes cell death of silk hair cells but did not affect early pollen tube growth inside the silk. Late pollen tube growth arrest was observed, leading to sterility. Heat stress causes elevated levels of reactive oxygen species (ROS) in silks, whose levels can be reduced by scavengers partly restoring pollen tube growth and fertility. A number of biological processes including hydrogen peroxide catabolic processes and bHLH transcription factor genes are downregulated by heat stress, while some NAC transcription factor genes are strongly upregulated. In conclusion, this study now provides a basis to select genes for engineering heat-stress-tolerant grass crops during the pollination phase.

Temperature and light reverse the fertility of rice P/TGMS line ostms19 via reactive oxygen species homeostasis

P/TGMS (Photo/thermo-sensitive genic male sterile) lines are crucial resources for two-line hybrid rice breeding. Previous studies revealed that slow development is a general mechanism for sterility-fertility conversion of P/TGMS in Arabidopsis. However, the difference in P/TGMS genes between rice and Arabidopsis suggests the presence of a distinct P/TGMS mechanism in rice. In this study, we isolated a novel P/TGMS line, ostms19, which shows sterility under high-temperature conditions and fertility under low-temperature conditions. OsTMS19 encodes a novel pentatricopeptide repeat (PPR) protein essential for pollen formation, in which a point mutation GTA(Val) to GCA(Ala) leads to ostms19 P/TGMS phenotype. It is highly expressed in the tapetum and localized to mitochondria. Under high temperature or long-day photoperiod conditions, excessive ROS accumulation in ostms19 anthers during pollen mitosis disrupts gene expression and intine formation, causing male sterility. Conversely, under low temperature or short-day photoperiod conditions, ROS can be effectively scavenged in anthers, resulting in fertility restoration. This indicates that ROS homeostasis is critical for fertility conversion. This relationship between ROS homeostasis and fertility conversion has also been observed in other tested rice P/TGMS lines. Therefore, we propose that ROS homeostasis is a general mechanism for the sterility-fertility conversion of rice P/TGMS lines.

Micro- and nanoplastics in agricultural soils: Assessing impacts and navigating mitigation

Micro-/nanoplastic contamination in agricultural soils raises concerns on agroecosystems and poses potential health risks. Some of agricultural soils have received significant amounts of micro-/nanoplastics (MNPs) through plastic mulch film and biosolid applications. However, a comprehensive understanding of the MNP impacts on soils and plants remains elusive. The interaction between soil particles and MNPs is an extremely complex issue due to the different properties and heterogeneity of soils and the diverse characteristics of MNPs. Moreover, MNPs are a class of relatively new anthropogenic pollutants that may negatively affect plants and food. Herein, we presented a comprehensive review of the impacts of MNPs on the properties of soil and the growth of plants. We also discussed different strategies for mitigating or eliminating MNP contamination. Moreover, perspectives for future research on MNP contamination in the agricultural soils are also highlighted.

Abnormal Degraded Tapetum 1 (ADT1) is required for tapetal cell death and pollen development in rice

The timely degradation of tapetum, the innermost somatic anther cell layer in flowering plants, is critical for pollen development. Although several genes involved in tapetum development have been characterized, the molecular mechanisms underlying tapetum degeneration remain elusive. Here, we showed that mutation in Abnormal Degraded Tapetum 1 (ADT1) resulted in overaccumulation of Reactive Oxygen Species (ROS) and abnormal anther development, causing earlier tapetum Programmed Cell Death (PCD) and pollen abortion. ADT1 encodes a nuclear membrane localized protein, which is strongly expressed in the developing microspores and tapetal cells during early anther development. Moreover, ADT1 could interact with metallothionein MT2b, which was related to ROS scavenging and cell death regulation. These findings indicate that ADT1 is required for proper timing of tapetum PCD by regulating ROS homeostasis, expanding our understanding of the regulatory network of male reproductive development in rice.

BR regulates wheat root salt tolerance by maintaining ROS homeostasis

MAIN CONCLUSION

Trace amounts of epibrassinolide (EpiBL) could partially rescue wheat root length inhibition in salt-stressed situation by scavenging ROS, and ectopic expression of TaDWF4 or TaBAK1 enhances root salt tolerance in Arabidopsis by balancing ROS level. Salt stress often leads to ion toxicity and oxidative stress, causing cell structure damage and root development inhibition in plants. While prior research indicated the involvement of exogenous brassinosteroid (BR) in plant responses to salt stress, the precise cytological role and the function of BR in wheat root development under salt stress remain elusive. Our study demonstrates that 100 mM NaCl solution inhibits wheat root development, but 5 nM EpiBL partially rescues root length inhibition by decreasing H2O2 content, oxygen free radical (OFR) content, along with increasing the peroxidase (POD) and catalase (CAT) activities in salt-stressed roots. The qRT-PCR experiment also shows that expression of the ROS-scavenging genes (GPX2 and CAT2) increased in roots after applying BR, especially during salt stress situation. Transcriptional analysis reveals decreased expression of BR synthesis and root meristem development genes under salt stress in wheat roots. Differential expression gene (DEG) enrichment analysis highlights the significant impact of salt stress on various biological processes, particularly "hydrogen peroxide catabolic process" and "response to oxidative stress". Additionally, the BR biosynthesis pathway is enriched under salt stress conditions. Therefore, we investigated the involvement of wheat BR synthesis gene TaDWF4 and BR signaling gene TaBAK1 in salt stress responses in roots. Our results demonstrate that ectopic expression of TaDWF4 or TaBAK1 enhances salt tolerance in Arabidopsis by balancing ROS (Reactive oxygen species) levels in roots.

Reactive oxygen species are signaling molecules that modulate plant reproduction

Reactive oxygen species (ROS) can serve as signaling molecules that are essential for plant growth and development but abiotic stress can lead to ROS increases to supraoptimal levels resulting in cellular damage. To ensure efficient ROS signaling, cells have machinery to locally synthesize ROS to initiate cellular responses and to scavenge ROS to prevent it from reaching damaging levels. This review summarizes experimental evidence revealing the role of ROS during multiple stages of plant reproduction. Localized ROS synthesis controls the formation of pollen grains, pollen-stigma interactions, pollen tube growth, ovule development, and fertilization. Plants utilize ROS-producing enzymes such as respiratory burst oxidase homologs and organelle metabolic pathways to generate ROS, while the presence of scavenging mechanisms, including synthesis of antioxidant proteins and small molecules, serves to prevent its escalation to harmful levels. In this review, we summarized the function of ROS and its synthesis and scavenging mechanisms in all reproductive stages from gametophyte development until completion of fertilization. Additionally, we further address the impact of elevated temperatures induced ROS on impairing these reproductive processes and of flavonol antioxidants in maintaining ROS homeostasis to minimize temperature stress to combat the impact of global climate change on agriculture.

Arabidopsis HAPLESS13/AP-1µ is critical for pollen sac formation and tapetal function

The production of excess and viable pollen grains is critical for reproductive success of flowering plants. Pollen grains are produced within anthers, the male reproductive organ whose development involves precisely controlled cell differentiation, division, and intercellular communication. In Arabidopsis thaliana, specification of an archesporial cell (AC) at four corners of a developing anther, followed by programmed cell divisions, generates four pollen sacs, walled by four cell layers among which the tapetum is in close contact with developing microspores. Tapetum secretes callose-dissolving enzymes to release microspores at early stages and undergoes programmed cell death (PCD) to deliver nutrients and signals for microspore development at later stages. Except for transcription factors, plasma membrane (PM)-associated and secretory peptides have also been demonstrated to mediate anther development. Adaptor protein complexes (AP) recruit both cargos and coat proteins during vesicle trafficking. Arabidopsis AP-1µ/HAPLESS13 (HAP13) is a core component of AP-1 for protein sorting at the trans-Golgi network/early endosomes (TGN/EE). We report here that Arabidopsis HAP13 is critical for pollen sac formation and for sporophytic control of pollen production. Functional loss of HAP13 causes a reduction in pollen sac number. It also results in the dysfunction of tapetum such that secretory function of tapetum at early stages and PCD of tapetum at later stages are both compromised. We further show that the expression of SPL, the polar distribution of auxin maximum, as well as the asymmetric distribution of PIN1 are interfered in hap13 anthers, which in combination may lead to male sterility in hap13.

Reactive oxygen species: Multidimensional regulators of plant adaptation to abiotic stress and development

Reactive oxygen species (ROS) are produced as undesirable by-products of metabolism in various cellular compartments, especially in response to unfavorable environmental conditions, throughout the life cycle of plants. Stress-induced ROS production disrupts normal cellular function and leads to oxidative damage. To cope with excessive ROS, plants are equipped with a sophisticated antioxidative defense system consisting of enzymatic and non-enzymatic components that scavenge ROS or inhibit their harmful effects on biomolecules. Nonetheless, when maintained at relatively low levels, ROS act as signaling molecules that regulate plant growth, development, and adaptation to adverse conditions. Here, we provide an overview of current approaches for detecting ROS. We also discuss recent advances in understanding ROS signaling, ROS metabolism, and the roles of ROS in plant growth and responses to various abiotic stresses.

Arabidopsis BECLIN1-induced autophagy mediates reprogramming in tapetal programmed cell death by altering the gross cellular homeostasis

In flowering plants, the tapetum degeneration in post-meiotic anther occurs through developmental programmed cell death (dPCD), which is one of the most critical and sensitive steps for the proper development of male gametophytes and fertility. Yet the pathways of dPCD, its regulation, and its interaction with autophagy remain elusive. Here, we report that high-level expression of Arabidopsis autophagy-related gene BECLIN1 (BECN1 or AtATG6) in the tobacco tapetum prior to their dPCD resulted in developmental defects. BECN1 induces severe autophagy and multiple cytoplasm-to-vacuole pathways, which alters tapetal cell reactive oxygen species (ROS)-homeostasis that represses the tapetal dPCD. The transcriptome analysis reveals that BECN1- expression caused major changes in the pathway, resulting in altered cellular homeostasis in the tapetal cell. Moreover, BECN1-mediated autophagy reprograms the execution of tapetal PCD by altering the expression of the key developmental PCD marker genes: SCPL48, CEP1, DMP4, BFN1, MC9, EXI1, and Bcl-2 member BAG5, and BAG6. This study demonstrates that BECN1-mediated autophagy is inhibitory to the dPCD of the tapetum, but the severity of autophagy leads to autophagic death in the later stages. The delayed and altered mode of tapetal degeneration resulted in male sterility.

Gh4CL20/20A involved in flavonoid biosynthesis is essential for male fertility in cotton (Gossypium hirsutum L.)

Flavonoids have been shown to play an essential role in plant growth and fertility. 4-Coumarate CoA ligase (4CL) is one of the indispensable enzymes involved in the biosynthesis of flavonoids. However, the role of 4CL and flavonoids in impact on cotton fertility is still unknown. In this study, on the basis of identification of an additional Gh4CL gene, Gh4CL20A, by using an updated G. hirsutum genome, we found that Gh4CL20A and its homologous Gh4CL20 were preferentially expressed in petals and stamens. The petals of the loss-of-function Gh4CL20/Gh4CL20A mutant generated by CRISPR/Cas9 gene editing remained white until wilting. Notably, the mutant showed indehiscent anthers, reduced number of pollen grains and pollen viability, leading to male sterility. Histological analysis revealed that abnormal degradation of anther tapetum at the tetrad stage and abnormal pollen grain development at the mature stage caused male sterility of the gene editing mutant. Analysis of the anther transcriptome identified a total of 10574 and 11962 genes up- and down-regulated in the mutant, respectively, compared to the wild-type. GO, KEGG, and WGCNA analyses linked the abnormality of the mutant anthers to the defective flavonoid biosynthetic pathway, leading to decreased activity of 4CL and chalcone isomerase (CHI) and reduced accumulation of flavonoids in the mutant. These results imply a role of Gh4CL20/Gh4CL20A in assuring proper development of cotton anthers by regulating flavonoid metabolism. This study elucidates a molecular mechanism underlying cotton anther development and provides candidate genes for creating cotton male sterile germplasm that has the potential to be used in production of hybrid seeds.

R-SNARE protein YKT61 mediates root apical meristem cell division via BRASSINOSTEROID-INSENSITIVE1 recycling

Root growth is sustained by cell division and differentiation of the root apical meristem (RAM), in which brassinosteroid (BR) signaling mediated via the dynamic targeting of BRASSINOSTEROID-INSENSITIVE1 (BRI1) plays complex roles. BRI1 is constitutively secreted to the plasma membrane (PM), internalized, and recycled or delivered into vacuoles, whose PM abundance is critical for BR signaling. Vesicle-target membrane fusion is regulated by heterotetrameric SNARE complexes. SNARE proteins have been implicated in BRI1 targeting, but how SNAREs affect RAM development is unclear. We report that Arabidopsis (Arabidopsis thaliana) YKT61, an atypical R-SNARE protein, is critical for BR-controlled RAM development through the dynamic targeting of BRI1. Functional loss of YKT61 is lethal for both male and female gametophytes. By using weak mutant alleles of YKT61, ykt61-partially complemented (ykt61-pc), we show that YKT61 knockdown results in a reduction of RAM length due to reduced cell division, similar to that in bri1-116. YKT61 physically interacts with BRI1 and is critical for the dynamic recycling of BRI1 to the PM. We further determine that YKT61 is critical for the dynamic biogenesis of vacuoles, for the maintenance of Golgi morphology, and for endocytosis, which may have a broad effect on development. Endomembrane compartments connected via vesicular machinery, such as SNAREs, influence nuclear-controlled cellular activities such as division and differentiation by affecting the dynamic targeting of membrane proteins, supporting a retro-signaling pathway from the endomembrane system to the nucleus.

Identification of NADPH Oxidase Genes Crucial for Rice Multiple Disease Resistance and Yield Traits

Reactive oxygen species (ROS) act as a group of signaling molecules in rice functioning in regulation of development and stress responses. Respiratory burst oxidase homologues (Rbohs) are key enzymes in generation of ROS. However, the role of the nine Rboh family members was not fully understood in rice multiple disease resistance and yield traits. In this study, we constructed mutants of each Rboh genes and detected their requirement in rice multiple disease resistance and yield traits. Our results revealed that mutations of five Rboh genes (RbohA, RbohB, RbohE, RbohH, and RbohI) lead to compromised rice blast disease resistance in a disease nursery and lab conditions; mutations of five Rbohs (RbohA, RbohB, RbohC, RbohE, and RbohH) result in suppressed rice sheath blight resistance in a disease nursery and lab conditions; mutations of six Rbohs (RbohA, RbohB, RbohC, RbohE, RbohH and RbohI) lead to decreased rice leaf blight resistance in a paddy yard and ROS production induced by PAMPs and pathogen. Moreover, all Rboh genes participate in the regulation of rice yield traits, for all rboh mutants display one or more compromised yield traits, such as panicle number, grain number per panicle, seed setting rate, and grain weight, resulting in reduced yield per plant except rbohb and rbohf. Our results identified the Rboh family members involved in the regulation of rice resistance against multiple pathogens that caused the most serious diseases worldwide and provide theoretical supporting for breeding application of these Rbohs to coordinate rice disease resistance and yield traits.

The Arabidopsis GPI-anchored protein COBL11 is necessary for regulating pollen tube integrity

Pollen tube integrity is required for achieving double fertilization in angiosperms. The rapid alkalinization factor4/19-ANXUR1/2-Buddha's paper seal 1/2 (RALF4/19-ANX1/2-BUPS1/2)-complex-mediated signaling pathway is critical to maintain pollen tube integrity, but the underlying mechanisms regulating the polar localization and distribution of these complex members at the pollen tube tip remain unclear. Here, we find that COBRA-like protein 11 (COBL11) loss-of-function mutants display a low pollen germination ratio, premature pollen tube burst, and seed abortion in Arabidopsis. COBL11 could interact with RALF4/19, ANX1/2, and BUPS1/2, and COBL11 functional deficiency could result in the disrupted distribution of RALF4 and ANX1, altered cell wall composition, and decreased levels of reactive oxygen species in pollen tubes. In conclusion, COBL11 is a regulator of pollen tube integrity during polar growth, which is conducted by a direct interaction that ensures the correct localization and polar distribution of RALF4 and ANX1 at the pollen tube tip.

The E3 ubiquitin ligase CSIT1 regulates critical sterility-inducing temperature by ribosome-associated quality control to safeguard two-line hybrid breeding in rice

Two-line hybrid breeding can fully utilize heterosis in crops. In thermo-sensitive genic male sterile (TGMS) lines, low critical sterility-inducing temperature (CSIT) is vital to safeguard the production of two-line hybrid seeds in rice (Oryza sativa), but the molecular mechanism determining CSIT is unclear. Here, we report the cloning of CSIT1, which encodes an E3 ubiquitin ligase, and show that CSIT1 modulates the CSIT of thermo-sensitive genic male sterility 5 (tms5)-based TGMS lines through ribosome-associated quality control (RQC). Biochemical assays demonstrated that CSIT1 binds to the 80S ribosomes and ubiquitinates abnormal nascent polypeptides for degradation in the RQC process. Loss of CSIT1 function inhibits the possible damage of tms5 to the ubiquitination system and protein translation, resulting in enhanced accumulation of anther-related proteins such as catalase to suppress abnormal accumulation of reactive oxygen species and premature programmed cell death in the tapetum, thereby leading to a much higher CSIT in the tms5-based TGMS lines. Taken together, our findings reveal a regulatory mechanism of CSIT, providing new insights into RQC and potential targets for future two-line hybrid breeding.

ROS interplay between plant growth and stress biology: Challenges and future perspectives

In plants, reactive oxygen species (ROS) have emerged as a multifunctional signaling molecules that modulate diverse stress and growth responses. Earlier studies on ROS in plants primarily focused on its toxicity and ROS-scavenging processes, but recent findings are offering new insights on its role in signal perception and transduction. Further, the interaction of cell wall receptors, calcium channels, HATPase, protein kinases, and hormones with NADPH oxidases (respiratory burst oxidase homologues (RBOHs), provides concrete evidence that ROS regulates major signaling cascades in different cellular compartments related to stress and growth responses. However, at the molecular level there are many knowledge gaps regarding how these players influence ROS signaling and how ROS regulate them during growth and stress events. Furthermore, little is known about how plant sensors or receptors detect ROS under various environmental stresses and induce subsequent signaling cascades. In light of this, we provided an update on the role of ROS signaling in plant growth and stress biology. First, we focused on ROS signaling, its production and regulation by cell wall receptor like kinases. Next, we discussed the interplay between ROS, calcium and hormones, which forms a major signaling trio regulatory network of signal perception and transduction. We also provided an overview on ROS and nitric oxide (NO) crosstalk. Furthermore, we emphasized the function of ROS signaling in biotic, abiotic and mechanical stresses, as well as in plant growth and development. Finally, we conclude by highlighting challenges and future perspectives of ROS signaling in plants that warrants future investigation.

Barley TAPETAL DEVELOPMENT and FUNCTION1 (HvTDF1) gene reveals conserved and unique roles in controlling anther tapetum development in dicot and monocot plants

The anther tapetum helps control microspore release and essential components for pollen wall formation. TAPETAL DEVELOPMENT and FUNCTION1 (TDF1) is an essential R2R3 MYB tapetum transcription factor in Arabidopsis thaliana; however, little is known about pollen development in the temperate monocot barley. Here, we characterize the barley (Hordeum vulgare L.) TDF1 ortholog using reverse genetics and transcriptomics. Spatial/temporal expression analysis indicates HvTDF1 has tapetum-specific expression during anther stage 7/8. Homozygous barley hvtdf1 mutants exhibit male sterility with retarded tapetum development, delayed tapetum endomitosis and cell wall degeneration, resulting in enlarged, vacuolated tapetum surrounding collapsing microspores. Transient protein expression and dual-luciferase assays show TDF1 is a nuclear-localized, transcription activator, that directly activates osmotin proteins. Comparison of hvtdf1 transcriptome data revealed several pathways were delayed, endorsing the observed retarded anther morphology. Arabidopsis tdf1 mutant fertility was recovered by HvTDF1, supporting a conserved role for TDF1 in monocots and dicots. This indicates that tapetum development shares similarity between monocot and dicots; however, barley HvTDF1 appears to uniquely act as a modifier to activate tapetum gene expression pathways, which are subsequently also induced by other factors. Therefore, the absence of HvTDF1 results in delayed developmental progression rather than pathway failure, although inevitably still results in pollen degeneration.

Transcriptome analysis provides insight into the regulatory mechanisms underlying pollen germination recovery at normal high ambient temperature in wild banana (Musa itinerans)

Introduction

Cultivated banana are polyploid, with low pollen fertility, and most cultivars are male sterile, which leads to difficulties in banana breeding research. The selection of male parent with excellent resistance and pollen fertility is therefore essential for banana breeding. Wild banana (Musa itinerans) have developed many good characteristics during natural selection and constitute an excellent gene pool for breeding. Therefore, research on wild banana breeding is very important for banana breeding.

Results

In the current analysis, we examined the changes in viability of wild banana pollens at different temperatures by in vitro germination, and found that the germination ability of wild banana pollens cultured at 28°C for 2 days was higher than that of pollens cultured at 23°C (pollens that could not germinate normally under low temperature stress), 24°C (cultured at a constant temperature for 2 days) and 32°C (cultured at a constant temperature for 2 days). To elucidate the molecular mechanisms underlying the germination restoration process in wild banana pollens, we selected the wild banana pollens that had lost its germination ability under low temperature stress (23°C) as the control group (CK) and the wild banana pollens that had recovered its germination ability under constant temperature incubation of 28°C for 2 days as the treatment group (T) for transcriptome sequencing. A total of 921 differentially expressed genes (DEGs) were detected in CK vs T, of which 265 were up-regulated and 656 were down-regulated. The combined analysis of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed that the activation, metabolism of various substances (lipids, sugars, amino acids) play a major role in restoring pollen germination capacity. TCA cycle and the sesquiterpenoid and triterpenoid biosynthetic pathways were also significantly enriched in the KEGG pathway. And we found that some DEGs may be associated with pollen wall formation, DNA methylation and DNA repair. The cysteine content, free fatty acid (FFA) content, H2O2 content, fructose content, and sucrose content of pollen were increased at treatment of 28°C, while D-Golactose content was decreased. Finally, the GO pathway was enriched for a total of 24 DEGs related to pollen germination, of which 16 DEGs received targeted regulation by 14 MYBs.

Discussions

Our study suggests that the balance between various metabolic processes, pollen wall remodelling, DNA methylation, DNA repairs and regulation of MYBs are essential for germination of wild banana pollens.

BOTRYOID POLLEN 1 regulates ROS-triggered PCD and pollen wall development by controlling UDP-sugar homeostasis in rice

Uridine diphosphate (UDP)-sugars are important metabolites involved in the biosynthesis of polysaccharides and may be important signaling molecules. UDP-glucose 4-epimerase (UGE) catalyzes the interconversion between UDP-Glc and UDP-Gal, whose biological function in rice (Oryza sativa) fertility is poorly understood. Here, we identify and characterize the botryoid pollen 1 (bp1) mutant and show that BP1 encodes a UGE that regulates UDP-sugar homeostasis, thereby controlling the development of rice anthers. The loss of BP1 function led to massive accumulation of UDP-Glc and imbalance of other UDP-sugars. We determined that the higher levels of UDP-Glc and its derivatives in bp1 may induce the expression of NADPH oxidase genes, resulting in a premature accumulation of reactive oxygen species (ROS), thereby advancing programmed cell death (PCD) of anther walls but delaying the end of tapetal degradation. The accumulation of UDP-Glc as metabolites resulted in an abnormal degradation of callose, producing an adhesive microspore. Furthermore, the UDP-sugar metabolism pathway is not only involved in the formation of intine but also in the formation of the initial framework for extine. Our results reveal how UDP-sugars regulate anther development and provide new clues for cellular ROS accumulation and PCD triggered by UDP-Glc as a signaling molecule.

Coping with the cold: unveiling cryoprotectants, molecular signaling pathways, and strategies for cold stress resilience

Low temperature stress significantly threatens crop productivity and economic sustainability. Plants counter this by deploying advanced molecular mechanisms to perceive and respond to cold stress. Transmembrane proteins initiate these responses, triggering a series of events involving secondary messengers such as calcium ions (Ca2+), reactive oxygen species (ROS), and inositol phosphates. Of these, calcium signaling is paramount, activating downstream phosphorylation cascades and the transcription of cold-responsive genes, including cold-regulated (COR) genes. This review focuses on how plants manage freeze-induced damage through dual strategies: cold tolerance and cold avoidance. Tolerance mechanisms involve acclimatization to decreasing temperatures, fostering gradual accumulation of cold resistance. In contrast, avoidance mechanisms rely on cryoprotectant molecules like potassium ions (K+), proline, glycerol, and antifreeze proteins (AFPs). Cryoprotectants modulate intracellular solute concentration, lower the freezing point, inhibit ice formation, and preserve plasma membrane fluidity. Additionally, these molecules demonstrate antioxidant activity, scavenging ROS, preventing protein denaturation, and subsequently mitigating cellular damage. By forming extensive hydrogen bonds with water molecules, cryoprotectants also limit intercellular water movement, minimizing extracellular ice crystal formation, and cell dehydration. The deployment of cryoprotectants is a key adaptive strategy that bolsters plant resilience to cold stress and promotes survival in freezing environments. However, the specific physiological and molecular mechanisms underlying these protective effects remain insufficiently understood. Therefore, this review underscores the need for further research to elucidate these mechanisms and assess their potential impact on crop productivity and sustainability, contributing to the progressive discourse in plant biology and environmental science.

ZmMS1/ZmLBD30-orchestrated transcriptional regulatory networks precisely control pollen exine development

Because of its significance for plant male fertility and, hence, direct impact on crop yield, pollen exine development has inspired decades of scientific inquiry. However, the molecular mechanism underlying exine formation and thickness remains elusive. In this study, we identified that a previously unrecognized repressor, ZmMS1/ZmLBD30, controls proper pollen exine development in maize. Using an ms1 mutant with aberrantly thickened exine, we cloned a male-sterility gene, ZmMs1, which encodes a tapetum-specific lateral organ boundary domain transcription factor, ZmLBD30. We showed that ZmMs1/ZmLBD30 is initially turned on by a transcriptional activation cascade of ZmbHLH51-ZmMYB84-ZmMS7, and then it serves as a repressor to shut down this cascade via feedback repression to ensure timely tapetal degeneration and proper level of exine. This activation-feedback repression loop regulating male fertility is conserved in maize and sorghum, and similar regulatory mechanism may also exist in other flowering plants such as rice and Arabidopsis. Collectively, these findings reveal a novel regulatory mechanism of pollen exine development by which a long-sought master repressor of upstream activators prevents excessive exine formation.

ROS accumulation-induced tapetal PCD timing changes leads to microspore abortion in cotton CMS lines

BACKGROUND

Cytoplasmic male sterility (CMS) is the basis of heterosis exploitation. CMS has been used to hybrid production in cotton, but its molecular mechanism remains unclear. CMS is associated with advanced or delayed tapetal programmed cell death (PCD), and reactive oxygen species (ROS) may mediate this process. In this study, we obtained Jin A and Yamian A, two CMS lines with different cytoplasmic sources.

RESULTS

Compared with maintainer Jin B, Jin A anthers showed advanced tapetal PCD with DNA fragmentation, producing excessive ROS which accumulated around the cell membrane, intercellular space and mitochondrial membrane. The activities of peroxidase (POD) and catalase (CAT) enzymes which can scavenge ROS were significantly decreased. However, Yamian A tapetal PCD was delayed with lower ROS content, and the activities of superoxide dismutase (SOD) and POD were higher than its maintainer. These differences in ROS scavenging enzyme activities may be caused by isoenzyme gene expressions. In addition, we found the excess ROS generated in Jin A mitochondria and ROS overflow from complex III might be the source in parallel with the reduction of ATP content.

CONCLUSION

ROS accumulation or abrogation were mainly caused by the joint action of ROS generation and scavenging enzyme activities transformation, which led to the abnormal progression of tapetal PCD, affected the development of microspores, and eventually contributed to male sterility. In Jin A, tapetal PCD in advance might be caused by mitochondrial ROS overproduction, accompanied by energy deficiency. The above studies will provide new insights into the cotton CMS and guide the follow-up research ideas.

Salt Tolerant Gene 1 contributes to salt tolerance by maintaining photosystem II activity in maize

Salt stress is a major environmental factor limiting crop growth and productivity. Here, we show that Salt-Tolerant Gene 1 (ZmSTG1) contributes to salt tolerance by maintaining photosystem activity in maize. ZmSTG1 encodes an endoplasmic reticulum localized protein and retrotransposon insertion in the promoter region causes differential expression levels in maize inbred lines. Overexpression of ZmSTG1 improved plant growth vigor, and knockout of ZmSTG1 weakened plant growth under normal and salt stress conditions. Transcriptome and metabolome analyses indicated that ZmSTG1 might regulate the expression of lipid trafficking-related genes dependent on the abscisic acid (ABA) signaling pathway, thereby increasing the galactolipids and phospholipid concentrations in the photosynthetic membrane under salt stress. Chlorophyll fluorescence parameters showed that the knockout of ZmSTG1 led to significant impairment of plant photosystem II (PSII) activity under normal and salt stress conditions, whereas overexpression of ZmSTG1 dramatically improved plant PSII activity under salt stress conditions. We also demonstrated that the application of the salt-tolerant locus could enhance salt tolerance in hybrid maize plants. Taken together, we propose that ZmSTG1 may modulate the lipid composition in the photosynthetic membrane by affecting the expression of lipid trafficking-related genes to maintain the photosynthetic activity of plants under salt stress.

Genomic survey of high-throughput RNA-Seq data implicates involvement of long intergenic non-coding RNAs (lincRNAs) in cytoplasmic male-sterility and fertility restoration in pigeon pea

BACKGROUND

Long-intergenic non-coding RNAs (lincRNAs) originate from intergenic regions and have no coding potential. LincRNAs have emerged as key players in the regulation of various biological processes in plant development. Cytoplasmic male-sterility (CMS) in association with restorer-of-fertility (Rf) systems makes it a highly reliable tool for exploring heterosis for producing commercial hybrid seeds. To date, there have been no reports of lincRNAs during pollen development in CMS and fertility restorer lines in pigeon pea.

OBJECTIVE

Identification of lincRNAs in the floral buds of cytoplasmic male-sterile (AKCMS11) and fertility restorer (AKPR303) pigeon pea lines.

METHODS

We employed a computational approach to identify lincRNAs in the floral buds of cytoplasmic male-sterile (AKCMS11) and fertility restorer (AKPR303) pigeon pea lines using RNA-Seq data.

RESULTS

We predicted a total of 2145 potential lincRNAs of which 966 were observed to be differentially expressed between the sterile and fertile pollen. We identified, 927 cis-regulated and 383 trans-regulated target genes of the lincRNAs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of the target genes revealed that these genes were specifically enriched in pathways like pollen and pollen tube development, oxidative phosphorylation, etc. We detected 23 lincRNAs that were co-expressed with 17 pollen-related genes with known functions. Fifty-nine lincRNAs were predicted to be endogenous target mimics (eTMs) for 25 miRNAs, and found to be associated with pollen development. The, lincRNA regulatory networks revealed that different lincRNA-miRNA-mRNA networks might be associated with CMS and fertility restoration.

CONCLUSION

Thus, this study provides valuable information by highlighting the functions of lincRNAs as regulators during pollen development in pigeon pea and utilization in hybrid seed production.

Ascorbic acid-mediated reactive oxygen species homeostasis modulates the switch from tapetal cell division to cell differentiation in Arabidopsis

The major antioxidant L-ascorbic acid (AsA) plays important roles in plant growth, development, and stress responses. However, the importance of AsA concentration and the regulation of AsA metabolism in plant reproduction remain unclear. In Arabidopsis (Arabidopsis thaliana) anthers, the tapetum monolayer undergoes cell differentiation to support pollen development. Here, we report that a transcription factor, DEFECTIVE IN TAPETAL DEVELOPMENT AND FUNCTION 1 (TDF1), inhibits tapetal cell division leading to cell differentiation. We identified SKEWED5-SIMILAR 18 (SKS18) as a downstream target of TDF1. Enzymatic assays showed that SKS18, annotated as a multicopper oxidase-like protein, has ascorbate oxidase activity, leading to AsA oxidation. We also show that VITAMIN C DEFECTIVE1 (VTC1), an AsA biosynthetic enzyme, is negatively controlled by TDF1 to maintain proper AsA contents. Consistently, either knockout of SKS18 or VTC1 overexpression raised AsA concentrations, resulting in extra tapetal cells, while SKS18 overexpression in tdf1 or the vtc1-3 tdf1 double mutant mitigated their defective tapetum. We observed that high AsA concentrations caused lower accumulation of reactive oxygen species (ROS) in tapetal cells. Overexpression of ROS scavenging genes in tapetum restored excess cell divisions. Thus, our findings demonstrate that TDF1-regulated AsA balances cell division and cell differentiation in the tapetum through governing ROS homeostasis.

Evolutionary Analysis of Respiratory Burst Oxidase Homolog (RBOH) Genes in Plants and Characterization of ZmRBOHs

The respiratory burst oxidase homolog (RBOH), as the key producer of reactive oxygen species (ROS), plays an essential role in plant development. In this study, a bioinformatic analysis was performed on 22 plant species, and 181 RBOH homologues were identified. A typical RBOH family was identified only in terrestrial plants, and the number of RBOHs increased from non-angiosperms to angiosperms. Whole genome duplication (WGD)/segmental duplication played a key role in RBOH gene family expansion. Amino acid numbers of 181 RBOHs ranged from 98 to 1461, and the encoded proteins had molecular weights from 11.1 to 163.6 kDa, respectively. All plant RBOHs contained a conserved NADPH_Ox domain, while some of them lacked the FAD_binding_8 domain. Plant RBOHs were classified into five main subgroups by phylogenetic analysis. Most RBOH members in the same subgroup showed conservation in both motif distribution and gene structure composition. Fifteen ZmRBOHs were identified in maize genome and were positioned in eight maize chromosomes. A total of three pairs of orthologous genes were found in maize, including ZmRBOH6/ZmRBOH8, ZmRBOH4/ZmRBOH10 and ZmRBOH15/ZmRBOH2. A Ka/Ks calculation confirmed that purifying selection was the main driving force in their evolution. ZmRBOHs had typical conserved domains and similar protein structures. cis-element analyses together with the expression profiles of the ZmRBOH genes in various tissues and stages of development suggested that ZmRBOH was involved in distinct biological processes and stress responses. Based on the RNA-Seq data and qRT-PCR analysis, the transcriptional response of ZmRBOH genes was examined under various abiotic stresses, and most of ZmRBOH genes were up-regulated by cold stress. These findings provide valuable information for further revealing the biological roles of ZmRBOH genes in plant development and abiotic stress responses.

GUS Reporter-Aided Promoter Deletion Analysis of A. thaliana POLYAMINE OXIDASE 3

Polyamine oxidases (PAOs) have been correlated with numerous physiological and developmental processes, as well as responses to biotic and abiotic stress conditions. Their transcriptional regulation is driven by signals generated by various developmental and environmental cues, including phytohormones. However, the inductive mechanism(s) of the corresponding genes remains elusive. Out of the five previously characterized Arabidopsis PAO genes, none of their regulatory sequences have been analyzed to date. In this study, a GUS reporter-aided promoter deletion approach was used to investigate the transcriptional regulation of AtPAO3 during normal growth and development as well as under various inductive environments. AtPAO3 contains an upstream open reading frame (uORF) and a short inter-cistronic sequence, while the integrity of both appears to be crucial for the proper regulation of gene expression. The full-length promoter contains several cis-acting elements that regulate the tissue-specific expression of AtPAO3 during normal growth and development. Furthermore, a number of TFBS that are involved in gene induction under various abiotic stress conditions display an additive effect on gene expression. Taken together, our data indicate that the transcription of AtPAO3 is regulated by multiple environmental factors, which probably work alongside hormonal signals and shed light on the fine-tuning mechanisms of PAO regulation.

The tapetal tissue is essential for the maintenance of redox homeostasis during microgametogenesis in tomato

The tapetum is a specialized layer of cells within the anther, adjacent to the sporogenous tissue. During its short life, it provides nutrients, molecules and materials to the pollen mother cells and microsporocytes, being essential during callose degradation and pollen wall formation. The interaction between the tapetum and sporogenous cells in Solanum lycopersicum (tomato) plants, despite its importance for breeding purposes, is poorly understood. To investigate this process, gene editing was used to generate loss-of-function mutants that showed the complete and specific absence of tapetal cells. These plants were obtained targeting the previously uncharacterized Solyc03g097530 (SlTPD1) gene, essential for tapetum specification in tomato plants. In the absence of tapetum, sporogenous cells developed and callose deposition was observed. However, sporocytes failed to undergo the process of meiosis and finally degenerated, leading to male sterility. Transcriptomic analysis conducted in mutant anthers lacking tapetum revealed the downregulation of a set of genes related to redox homeostasis. Indeed, mutant anthers showed a reduction in the accumulation of reactive oxygen species (ROS) at early stages and altered activity of ROS-scavenging enzymes. The results obtained highlight the importance of the tapetal tissue in maintaining redox homeostasis during male gametogenesis in tomato plants.

The interaction of ABA and ROS in plant growth and stress resistances

The plant hormone ABA (abscisic acid) plays an extremely important role in plant growth and adaptive stress, including but are not limited to seed germination, stomatal closure, pathogen infection, drought and cold stresses. Reactive oxygen species (ROS) are response molecules widely produced by plant cells under biotic and abiotic stress conditions. The production of apoplast ROS is induced and regulated by ABA, and participates in the ABA signaling pathway and its regulated plant immune system. In this review, we summarize ABA and ROS in apoplast ROS production, plant response to biotic and abiotic stresses, plant growth regulation, ABA signal transduction, and the regulatory relationship between ABA and other plant hormones. In addition, we also discuss the effects of protein post-translational modifications on ABA and ROS related factors.

Comparative Transcriptome Analysis Reveals Key Insights into Fertility Conversion in the Thermo-Sensitive Cytoplasmic Male Sterile Wheat

Thermo-sensitive cytoplasmic male sterility (TCMS) plays a crucial role in hybrid production and hybrid breeding; however, there are few studies on molecular mechanisms related to anther abortion in the wheat TCMS line. In this study, FA99, a new wheat thermo-sensitive cytoplasmic male sterility line, was investigated. Fertility conversion analysis showed that FA99 was mainly controlled by temperature, and the temperature-sensitive stage was pollen mother cell formation to a uninucleate stage. Further phenotypic identification and paraffin section showed that FA99 was characterized by indehiscent anthers and aborted pollen in a sterile environment and tapetum was degraded prematurely during the tetrad period, which was the critical abortion period of FA99. The contents of O^2-, H₂O₂, MDA and POD were significantly changed in FA99 under a sterile environment by the determination of physiological indexes. Furthermore, through transcriptome analysis, 252 differentially expressed genes were identified, including 218 downregulated and 34 upregulated genes. Based on KOG function classification, GO enrichment and KEGG pathways analysis, it was evident that significant transcriptomic changes in FA99 under different fertility environments, and the major differences were "phenylalanine metabolism", "phenylpropanoid biosynthesis", "cutin, suberine and wax biosynthesis", "phenylalanine, tyrosine and tryptophan biosynthesis" and "citrate cycle (TCA cycle)". Finally, we proposed an intriguing transcriptome-mediated pollen abortion and male sterility network for FA99. These findings provided data on the molecular mechanism of fertility conversion in thermo-sensitive cytoplasmic male sterility wheat.

Anther development in Arabidopsis thaliana involves symplastic isolation and apoplastic gating of the tapetum-middle layer interface

During flowering plant reproduction, anthers produce pollen grains, the development of which is supported by the tapetum, a nourishing maternal tissue that also contributes non-cell-autonomously to the pollen wall, the resistant external layer on the pollen surface. How the anther restricts movement of the tapetum-derived pollen wall components, while allowing metabolites such as sugars and amino acids to reach the developing pollen, remains unknown. Here, we show experimentally that in arabidopsis thaliana the tapetum and developing pollen are symplastically isolated from each other, and from other sporophytic tissues, from meiosis onwards. We show that the peritapetal strip, an apoplastic structure, separates the tapetum and the pollen grains from other anther cell layers and can prevent the apoplastic diffusion of fluorescent proteins, again from meiosis onwards. The formation and selective barrier functions of the peritapetal strip require two NADPH oxidases, RBOHE and RBOHC, which play a key role in pollen formation. Our results suggest that, together with symplastic isolation, gating of the apoplast around the tapetum may help generate metabolically distinct anther compartments.

Maize sterility gene DRP1 encodes a desiccation-related protein that is critical for Ubisch bodies and pollen exine development

Desiccation tolerance is a remarkable feature of pollen, seeds, and resurrection-type plants. Exposure to desiccation stress can cause sporophytic defects, resulting in male sterility. Here, we report the novel maize sterility gene DRP1 (Desiccation-Related Protein 1), which was identified by bulked-segregant analysis sequencing and encodes a desiccation-related protein. Loss of function of DRP1 results in abnormal Ubisch bodies, defective tectum of the pollen exine, and complete male sterility. Our results suggest that DRP1 may facilitate anther dehydration to maintain appropriate water status. DRP1 is a secretory protein that is specifically expressed in the tapetum and microspore from the tetrad to the uninucleate microspore stage. Differentially expressed genes in drp1 are enriched in Gene Ontology terms for pollen exine formation, polysaccharide catabolic process, extracellular region, and response to heat. In addition, DRP1 is a target of selection that appears to have played an important role in the spread of maize from tropical/subtropical to temperate regions. Taken together, our results suggest that DRP1 encodes a desiccation-related protein whose loss of function causes male sterility. Our findings provide a potential genetic resource that may be used to design crops for heterosis utilization.

OsMADS58 Stabilizes Gene Regulatory Circuits during Rice Stamen Development

Rice (Oryza sativa) OsMADS58 is a C-class MADS box protein, and characterization of a transposon insertion mutant osmads58 suggested that OsMADS58 plays a role in stamen development. However, as no null mutation has been obtained, its role has remained unclear. Here, we report that the CRISPR knockout mutant osmads58 exhibits complex altered phenotypes, including anomalous diploid germ cells, aberrant meiosis, and delayed tapetum degeneration. This CRISPR mutant line exhibited stronger changes in expression of OsMADS58 target genes compared with the osmads58 dSpm (transposon insertion) line, along with changes in multiple pathways related to early stamen development. Notably, transcriptional regulatory circuits in young panicles covering the stamen at stages 4-6 were substantially altered in the CRISPR line compared to the dSpm line. These findings strongly suggest that the pleiotropic effects of OsMADS58 on stamen development derive from a potential role in stabilizing gene regulatory circuits during early stamen development. Thus, this work opens new avenues for viewing and deciphering the regulatory mechanisms of early stamen development from a network perspective.

Mutation of glucose-methanol-choline oxidoreductase leads to thermosensitive genic male sterility in rice and Arabidopsis

Thermosensitive genic male sterility (TGMS) lines serve as the major genetic resource for two-line hybrid breeding in rice. However, their unstable sterility under occasional low temperatures in summer highly limits their application. In this study, we identified a novel rice TGMS line, ostms18, of cultivar ZH11 (Oryza sativa ssp. japonica). ostms18 sterility is more stable in summer than the TGMS line carrying the widely used locus tms5 in the ZH11 genetic background, suggesting its potential application for rice breeding. The ostms18 TGMS trait is caused by the point mutation from Gly to Ser in a glucose-methanol-choline (GMC) oxidoreductase; knockout of the oxidoreductase was previously reported to cause complete male sterility. Cellular analysis revealed the pollen wall of ostms18 to be defective, leading to aborted pollen under high temperature. Further analysis showed that the tapetal transcription factor OsMS188 directly regulates OsTMS18 for pollen wall formation. Under low temperature, the flawed pollen wall in ostms18 is sufficient to protect its microspore, allowing for development of functional pollen and restoring fertility. We identified the orthologous gene in Arabidopsis. Although mutants for the gene were fertile under normal conditions (24°C), fertility was significantly reduced under high temperature (28°C), exhibiting a TGMS trait. A cellular mechanism integrated with genetic mutations and different plant species for fertility restoration of TGMS lines is proposed.

TaEXPB5 functions as a gene related to pollen development in thermo-sensitive male-sterility wheat with Aegilops kotschyi cytoplasm

The thermo-sensitive cytoplasmic male-sterility line with Aegilops kotschyi cytoplasm (K-TCMS) is completely male sterile under low temperature (< 18 ℃) during Zadoks growth stages 45-52, whereas its fertility can be restored under hot temperature (≥ 20 ℃). The K-TCMS line may facilitate hybrid breeding and hybrid wheat production. Therefore, to elucidate the molecular mechanisms of its male sterility/fertility conversion, we conducted the association analysis of proteins and transcript expression to screen fertility related genes using RNA-seq, iTRAQ, and PRM-based assay. A gene encoding expansin protein in wheat, TaEXPB5, was isolated in K-TCMS line KTM3315A, which upregulated expression in the fertility anthers. Subcellular localization analysis suggested that TaEXPB5 protein localized to nucleus and cell wall. The silencing of TaEXPB5 displayed pollen abortion and the declination of fertility. Further, cytological investigation indicated that the silencing of TaEXPB5 induced the early degradation of tapetum and abnormal development of pollen wall. These results implied that TaEXPB5 may be essential for anther or pollen development and male fertility of KTM3315A. These findings provide a novel insight into molecular mechanism of fertility conversion for thermo-sensitive cytoplasmic male-sterility wheat, and contribute to the molecular breeding of hybrid wheat in the future.

Multiple forms of vitamin B6 regulate salt tolerance by balancing ROS and abscisic acid levels in maize root

Salt stress causes osmotic stress, ion toxicity and oxidative stress, inducing the accumulation of abscisic acid (ABA) and excessive reactive oxygen species (ROS) production, which further damage cell structure and inhibit the development of roots in plants. Previous study showed that vitamin B6 (VB6) plays a role in plant responses to salt stress, however, the regulatory relationship between ROS, VB6 and ABA under salt stress remains unclear yet in plants. In our study, we found that salt stress-induced ABA accumulation requires ROS production, in addition, salt stress also promoted VB6 (including pyridoxamine (PM), pyridoxal (PL), pyridoxine (PN), and pyridoxal 5'-phosphate (PLP)) accumulation, which involved in ROS scavenging and ABA biosynthesis. Furthermore, VB6-deficient maize mutant small kernel2 (smk2) heterozygous is more susceptible to salt stress, and which failed to scavenge excessive ROS effectively or induce ABA accumulation in maize root under salt stress, interestingly, which can be restored by exogenous PN and PLP, respectively. According to these results, we proposed that PN and PLP play an essential role in balancing ROS and ABA levels under salt stress, respectively, it laid a foundation for VB6 to be better applied in crop salt resistance than ABA.

Endophytic extract Zhinengcong alleviates heat stress-induced reproductive defect in Solanum lycopersicum

High temperature negatively affects reproductive process significantly, leading to tremendous losses in crop quality and yield. Zhinengcong (ZNC), a crude extract from the endophytic fungus Paecilomyces variotii, has been shown to improve plant growth and resistance to biotic and abiotic stresses. We show here that ZNC can also alleviate heat stress-induced reproductive defects in Solanum lycopersicum, such as short-term heat-induced inhibition on pollen viability, germination and tube growth, and long-term heat stress-induced pollen developmental defects. We further demonstrated that ZNC alleviates heat stress by downregulating the expressions of ROS production-related genes, RBOHs, and upregulating antioxidant related genes and the activities of the corresponding enzymes, thus preventing the over accumulation of heat-induced reactive oxygen species (ROS) in anther, pollen grain and pollen tube. Furthermore, spraying application of ZNC onto tomato plants under long-term heat stress promotes fruit and seed bearing in the field. In summary, plant endophytic fungus extract ZNC promotes the reproductive process and yield of tomato plants under heat stress and presents excellent potential in agricultural applications.

Halophyte Nitraria billardieri CIPK25 mitigates salinity-induced cell damage by alleviating H2O2 accumulation

The plant-specific module of calcineurin B-like proteins (CBLs) and CBL-interacting protein kinases (CIPKs) play a crucial role in plant adaptation to different biotic and abiotic stresses in various plant species. Despite the importance of the CBL-CIPK module in regulating plant salt tolerance, few halophyte CIPK orthologs have been studied. We identified NbCIPK25 in the halophyte Nitraria billardieri as a salt-responsive gene that may improve salt tolerance in glycophytes. Sequence analyses indicated that NbCIPK25 is a typical CIPK family member with a conserved NAF motif, which contains the amino acids: asparagine, alanine, and phenylalanine. NbCIPK25 overexpression in salt-stressed transgenic Arabidopsis seedlings resulted in enhanced tolerance to salinity, a higher survival rate, longer newly grown roots, more root meristem cells, and less damaged root cells in comparison to wild-type (WT) plants. H2O2 accumulation and malondialdehyde (MDA) content were both deceased in NbCIPK25-transgenic plants under salt treatment. Furthermore, their proline content, an important factor for scavenging reactive oxygen species, accumulated at a significantly higher level. In concordance, the transcription of genes related to proline accumulation was positively regulated in transgenic plants under salt condition. Finally, we observed a stronger auxin response in salt-treated transgenic roots. These results provide evidence for NbCIPK25 improving salt tolerance by mediating scavenging of reactive oxygen species, thereby protecting cells from oxidation and maintaining plant development under salt stress. These findings suggest the potential application of salt-responsive NbCIPK25 for cultivating glycophytes with a higher salt tolerance through genetic engineering.

Receptor for Activated C Kinase1B (OsRACK1B) Impairs Fertility in Rice through NADPH-Dependent H2O2 Signaling Pathway

The scaffold protein receptor for Activated C Kinase1 (RACK1) regulates multiple aspects of plants, including seed germination, growth, environmental stress responses, and flowering. Recent studies have revealed that RACK1 is associated with NADPH-dependent reactive oxygen species (ROS) signaling in plants. ROS, as a double-edged sword, can modulate several developmental pathways in plants. Thus, the resulting physiological consequences of perturbing the RACK1 expression-induced ROS balance remain to be explored. Herein, we combined molecular, pharmacological, and ultrastructure analysis approaches to investigate the hypothesized connection using T-DNA-mediated activation-tagged RACK1B overexpressed (OX) transgenic rice plants. In this study, we find that OsRACK1B-OX plants display reduced pollen viability, defective anther dehiscence, and abnormal spikelet morphology, leading to partial spikelet sterility. Microscopic observation of the mature pollen grains from the OX plants revealed abnormalities in the exine and intine structures and decreased starch granules in the pollen, resulting in a reduced number of grains per locule from the OX rice plants as compared to that of the wild-type (WT). Histochemical staining revealed a global increase in hydrogen peroxide (H₂O₂) in the leaves and roots of the transgenic lines overexpressing OsRACK1B compared to that of the WT. However, the elevated H₂O₂ in tissues from the OX plants can be reversed by pre-treatment with diphenylidonium (DPI), an NADPH oxidase inhibitor, indicating that the source of H₂O₂ could be, in part, NADPH oxidase. Expression analysis showed a differential expression of the NADPH/respiratory burst oxidase homolog D (RbohD) and antioxidant enzyme-related genes, suggesting a homeostatic mechanism of H₂O₂ production and antioxidant enzyme activity. BiFC analysis demonstrated that OsRACK1B interacts with the N-terminal region of RbohD in vivo. Taken together, these data indicate that elevated OsRACK1B accumulates a threshold level of ROS, in this case H₂O₂, which negatively regulates pollen development and fertility. In conclusion, we hypothesized that an optimal expression of RACK1 is critical for fertility in rice plants.

The Loss-Function of the Male Sterile Gene ZmMs33/ZmGPAT6 Results in Severely Oxidative Stress and Metabolic Disorder in Maize Anthers

In plants, oxidative stress and metabolic reprogramming frequently induce male sterility, however our knowledge of the underlying molecular mechanism is far from complete. Here, a maize genic male-sterility (GMS) mutant (ms33-6038) with a loss-of-function of the ZmMs33 gene encoding glycerol-3-phosphate acyltransferase 6 (GPAT6) displayed severe deficiencies in the development of a four-layer anther wall and microspores and excessive reactive oxygen species (ROS) content in anthers. In ms33-6038 anthers, transcriptome analysis identified thousands of differentially expressed genes that were functionally enriched in stress response and primary metabolism pathways. Further investigation revealed that 64 genes involved in ROS production, scavenging, and signaling were specifically changed in expression levels in ms33-6038 anthers compared to the other five investigated GMS lines. The severe oxidative stress triggered premature tapetal autophagy and metabolic reprogramming mediated mainly by the activated SnRK1-bZIP pathway, as well as the TOR and PP2AC pathways, proven by transcriptome analysis. Furthermore, 20 reported maize GMS genes were altered in expression levels in ms33-6038 anthers. The excessive oxidative stress and the metabolic reprogramming resulted in severe phenotypic deficiencies in ms33-6038 anthers. These findings enrich our understanding of the molecular mechanisms by which ROS and metabolic homeostasis impair anther and pollen development in plants.