OsRPK1, a novel leucine-rich repeat receptor-like kinase, negatively regulates polar auxin transport and root development in rice

An update on evolutionary, structural, and functional studies of receptor-like kinases in plants

All living organisms must develop mechanisms to cope with and adapt to new environments. The transition of plants from aquatic to terrestrial environment provided new opportunities for them to exploit additional resources but made them vulnerable to harsh and ever-changing conditions. As such, the transmembrane receptor-like kinases (RLKs) have been extensively duplicated and expanded in land plants, increasing the number of RLKs in the advanced angiosperms, thus becoming one of the largest protein families in eukaryotes. The basic structure of the RLKs consists of a variable extracellular domain (ECD), a transmembrane domain (TM), and a conserved kinase domain (KD). Their variable ECDs can perceive various kinds of ligands that activate the conserved KD through a series of auto- and trans-phosphorylation events, allowing the KDs to keep the conserved kinase activities as a molecular switch that stabilizes their intracellular signaling cascades, possibly maintaining cellular homeostasis as their advantages in different environmental conditions. The RLK signaling mechanisms may require a coreceptor and other interactors, which ultimately leads to the control of various functions of growth and development, fertilization, and immunity. Therefore, the identification of new signaling mechanisms might offer a unique insight into the regulatory mechanism of RLKs in plant development and adaptations. Here, we give an overview update of recent advances in RLKs and their signaling mechanisms.

Uncovering the Genomic Regions Associated with Yield Maintenance in Rice Under Drought Stress Using an Integrated Meta-Analysis Approach

The complex trait of yield is controlled by several quantitative trait loci (QTLs). Given the global water deficit issue, the development of rice varieties suitable for non-flooded cultivation holds significant importance in breeding programs. The powerful approach of Meta-QTL (MQTL) analysis can be used for the genetic dissection of complicated quantitative traits. In the current study, a comprehensive MQTL analysis was conducted to identify consistent QTL regions associated with drought tolerance and yield-related traits under water deficit conditions in rice. In total, 1087 QTLs from 134 rice populations, published between 2000 to 2021, were utilized in the analysis. Distinct MQTL analysis of the relevant traits resulted in the identification of 213 stable MQTLs. The confidence interval (CI) for the detected MQTLs was between 0.12 and 19.7 cM. The average CI of the identified MQTLs (4.68 cM) was 2.74 times narrower compared to the average CI of the initial QTLs. Interestingly, 63 MQTLs coincided with SNP peak positions detected by genome-wide association studies for yield and drought tolerance-associated traits under water deficit conditions in rice. Considering the genes located both in the QTL-overview peaks and the SNP peak positions, 19 novel candidate genes were introduced, which are associated with drought response index, plant height, panicle number, biomass, and grain yield. Moreover, an inclusive MQTL analysis was performed on all the traits to obtain "Breeding MQTLs". This analysis resulted in the identification of 96 MQTLs with a CI ranging from 0.01 to 9.0 cM. The mean CI of the obtained MQTLs (2.33 cM) was 4.66 times less than the mean CI of the original QTLs. Thirteen MQTLs fulfilling the criteria of having more than 10 initial QTLs, CI < 1 cM, and an average phenotypic variance explained greater than 10%, were designated as "Breeding MQTLs". These findings hold promise for assisting breeders in enhancing rice yield under drought stress conditions.

Knocking Out OsRLK7-1 Impairs Rice Growth and Development but Enhances Its Resistance to Planthoppers

Leucine-rich repeat receptor-like kinases (LRR-RLKs) are an important subfamily of receptor-like kinases (RLKs) in plants that play key roles in sensing different biotic and abiotic stress. However, the role of LRR-RLKs in herbivore-induced plant defense remains largely elusive. Here, we found that the expression of a rice gene, OsRLK7-1, was induced by mechanical wounding, but was slightly suppressed by the infestation of gravid females of brown planthopper (BPH, Nilaparvata lugens) or white-backed planthopper (WBPH, Sogatella furcifera). Through targeted disruption of OsRLK7-1 (resulting in the ko-rlk lines), we observed an augmentation in transcript levels of BPH-induced OsMPK3, OsWRKY30, OsWRKY33, and OsWRKY45, alongside heightened levels of planthopper-induced jasmonic acid, JA-isoleucine, and abscisic acid in plant tissues. These dynamic changes further facilitated the biosynthesis of multiple phenolamides within the rice plants, culminating in an enhanced resistance to planthopper infestations under both lab and field conditions. In addition, knocking out OsRLK7-1 impaired plant growth and reproduction. These results suggest that OsRLK7-1 plays an important role in regulating rice growth, development, and rice-planthopper interactions.

The Germin-like protein gene OsGER4 is involved in heat stress response in rice root development

Rice (Oryza sativa L.) is one of the most important dietary carbohydrate sources for half of the world's population. However, it is not well adapted to environmental stress conditions, necessitating to create new and improved varieties to help ensure sufficient rice production in the face of rising populations and shrinking arable land. Recently, the development of the CRISPR/Cas9 gene editing system has allowed researchers to study functional genomics and engineer new rice varieties with great efficiency compared to conventional methods. In this study, we investigate the involvement of OsGER4, a germin-like protein identified by a genome-wide association study that is associated with rice root development under a stress hormone jasmonic acids treatment. Analysis of the OsGER4 promoter region revealed a series of regulatory elements that connect this gene to ABA signaling and water stress response. Under heat stress, osger4 mutant lines produce a significantly lower crown root than wild-type Kitaake rice. The loss of OsGER4 also led to the reduction of lateral root development. Using the GUS promoter line, OsGER4 expression was detected in the epidermis of the crown root primordial, in the stele of the crown root, and subsequently in the primordial of the lateral root. Taken together, these results illustrated the involvement of OsGER4 in root development under heat stress by regulating auxin transport through plasmodesmata, under control by both ABA and auxin signaling.

Genetic and Hormonal Blueprint of Shoot-Borne Adventitious Root Development in Rice and Maize

The evolution of root architecture in plants was a prerequisite for the absorption of water and minerals from the soil, and thus a major determinant of terrestrial plant colonization. Cereals have a remarkably complex root system consisting of embryonic primary roots and post-embryonic lateral roots and shoot-borne adventitious roots. Among grass species, rice adventitious roots (also called crown roots) are developed from compressed nodes at the stem base, whereas in maize, besides crown roots, several aboveground brace roots are also formed, thus adventitious root types display species-specific diversity. Despite being the backbone for the adult root system in monocots, adventitious roots are the least studied of all the plant organs. In recent times, molecular genetics, genomics and proteomics-based approaches have been utilized to dissect the mechanism of post-embryonic meristem formation and tissue patterning. Adventitious root development is a cumulative effect of the actions and interactions of crucial genetic and hormonal regulators. In this review, we provide a comprehensive view of the key regulators involved during the different stages of adventitious root development in two important crop plants, rice and maize. We have reviewed the roles of major phytohormones, microRNAs and transcription factors and their crosstalk during adventitious root development in these cereal crops.

Advances in Receptor-like Protein Kinases in Balancing Plant Growth and Stress Responses

Accompanying the process of growth and development, plants are exposed to ever-changing environments, which consequently trigger abiotic or biotic stress responses. The large protein family known as receptor-like protein kinases (RLKs) is involved in the regulation of plant growth and development, as well as in the response to various stresses. Understanding the biological function and molecular mechanism of RLKs is helpful for crop breeding. Research on the role and mechanism of RLKs has recently received considerable attention regarding the balance between plant growth and environmental adaptability. In this paper, we systematically review the classification of RLKs, the regulatory roles of RLKs in plant development (meristem activity, leaf morphology and reproduction) and in stress responses (disease resistance and environmental adaptation). This review focuses on recent findings revealing that RLKs simultaneously regulate plant growth and stress adaptation, which may pave the way for the better understanding of their function in crop improvement. Although the exact crosstalk between growth constraint and plant adaptation remains elusive, a profound study on the adaptive mechanisms for decoupling the developmental processes would be a promising direction for the future research.

The Germin-like protein OsGER4 is involved in promoting crown root development under exogenous jasmonic acid treatment in rice

In rice (Oryza sativa L.), crown roots (CRs) have many important roles in processes such as root system expansion, water and mineral uptake, and adaptation to environmental stresses. Phytohormones such as auxin, cytokinin, and ethylene are known to control CR initiation and development in rice. However, the role of jasmonic acid (JA) in CR development remained elusive. Here, we report that JA promotes CR development by regulating OsGER4, a rice Germin-like protein. Root phenotyping analysis revealed that exogenous JA treatment induced an increase in CR number in a concentration-dependent manner. A subsequent genome-wide association study and gene expression analyses pinpointed a strong association between the Germin-like protein OsGER4 and the increase in CR number under exogenous JA treatment. The ProGER4::GUS reporter line showed that OsGER4 is a hormone-responsive gene involved in various stress responses, mainly confined to epidermal and vascular tissues during CR primordia development and to vascular bundles of mature crown and lateral roots. Notable changes in OsGER4 expression patterns caused by the polar auxin transport inhibitor NPA support its connection to auxin signaling. Phenotyping experiments with OsGER4 knockout mutants confirmed that this gene is required for CR development under exogenous JA treatment. Overall, our results provide important insights into JA-mediated regulation of CR development in rice.

Resequencing of 558 Chinese mungbean landraces identifies genetic loci associated with key agronomic traits

Mungbean is a warm-season annual food legume and plays important role in supplying food and nutritional security in many tropical countries. However, the genetic basis of its agronomic traits remains poorly understood. Therefore, we resequenced 558 Chinese mungbean landraces and produced a comprehensive map of mungbean genomic variation. We phenotyped all landraces in six different environments. Genome-wide association studies (GWAS) produced 110 signals significantly associated with nine agronomic traits, for which several candidate genes were identified. Overall, this study provides new insight into the genetic architecture of mungbean agronomic traits. Moreover, the genome-wide variations identified here should be valuable resources for future breeding studies of this important food legume.

Root system architecture in rice: impacts of genes, phytohormones and root microbiota

To feed the continuously expanding world's population, new crop varieties have been generated, which significantly contribute to the world's food security. However, the growth of these improved plant varieties relies primarily on synthetic fertilizers, which negatively affect the environment and human health; therefore, continuous improvement is needed for sustainable agriculture. Several plants, including cereal crops, have the adaptive capability to combat adverse environmental changes by altering physiological and molecular mechanisms and modifying their root system to improve nutrient uptake efficiency. These plants operate distinct pathways at various developmental stages to optimally establish their root system. These processes include changes in the expression profile of genes, changes in phytohormone level, and microbiome-induced root system architecture (RSA) modification. Several studies have been performed to understand microbial colonization and their involvement in RSA improvement through changes in phytohormone and transcriptomic levels. This review highlights the impact of genes, phytohormones, and particularly root microbiota in influencing RSA and provides new insights resulting from recent studies on rice root as a model system and summarizes the current knowledge about biochemical and central molecular mechanisms.

Genome-Wide Identification and Characterization of Receptor-Like Protein Kinase 1 (RPK1) Gene Family in Triticum aestivum Under Drought Stress

Receptor-like protein kinase1 (RPK1) genes play crucial roles in plant growth and development processes, root architecture, and abiotic stress regulation. A comprehensive study of the RPK1 gene family has not been reported in bread wheat (Triticum aestivum). Here, we reported the genome-wide identification, characterization, and expression patterns of the RPK1 gene family in wheat. Results confirmed 15 TaRPK1 genes, classified mainly into three sub-clades based on a phylogenetic tree. The TaRPK1 genes were mapped on chromosomes 1–3 in the respective A, B, and D genomes. Gene structure, motif conservation, collinearity prediction, and synteny analysis were carried out systematically. A Gene ontology study revealed that TaRPK1 genes play a vital role during molecular and biological processes. We also identified 18 putative miRNAs targeting TaRPK1 genes, suggesting their roles in growth, development, and stress responses. Cis-Regulatory elements interpreted the presence of light-related elements, hormone responsiveness, and abiotic stress-related motifs in the promoter regions. The SWISS_MODEL predicted the successful models of TaRPK1 proteins with at least 30% identity to the template, a widely accepted threshold for successful modeling. In silico expression analysis in different tissues and stages suggested that TaRPK1 genes exhibited the highest expression in root tissues. Moreover, qRT-PCR further validated the higher expression of TaRPK1 genes in roots of drought-tolerant varieties compared to the drought-susceptible variety. Collectively, the present study renders valuable information on the functioning of TaRPK1 genes in wheat that will be useful in further functional validation of these genes in future studies.

Comparative Genomic Analysis of Quantitative Trait Loci Associated With Micronutrient Contents, Grain Quality, and Agronomic Traits in Wheat (Triticum aestivum L.)

Comparative genomics and meta-quantitative trait loci (MQTLs) analysis are important tools for the identification of reliable and stable QTLs and functional genes controlling quantitative traits. We conducted a meta-analysis to identify the most stable QTLs for grain yield (GY), grain quality traits, and micronutrient contents in wheat. A total of 735 QTLs retrieved from 27 independent mapping populations reported in the last 13 years were used for the meta-analysis. The results showed that 449 QTLs were successfully projected onto the genetic consensus map which condensed to 100 MQTLs distributed on wheat chromosomes. This consolidation of MQTLs resulted in a three-fold reduction in the confidence interval (CI) compared with the CI for the initial QTLs. Projection of QTLs revealed that the majority of QTLs and MQTLs were in the non-telomeric regions of chromosomes. The majority of micronutrient MQTLs were located on the A and D genomes. The QTLs of thousand kernel weight (TKW) were frequently associated with QTLs for GY and grain protein content (GPC) with co-localization occurring at 55 and 63%, respectively. The co- localization of QTLs for GY and grain Fe was found to be 52% and for QTLs of grain Fe and Zn, it was found to be 66%. The genomic collinearity within Poaceae allowed us to identify 16 orthologous MQTLs (OrMQTLs) in wheat, rice, and maize. Annotation of promising candidate genes (CGs) located in the genomic intervals of the stable MQTLs indicated that several CGs (e.g., TraesCS2A02G141400, TraesCS3B02G040900, TraesCS4D02G323700, TraesCS3B02G077100, and TraesCS4D02G290900) had effects on micronutrients contents, yield, and yield-related traits. The mapping refinements leading to the identification of these CGs provide an opportunity to understand the genetic mechanisms driving quantitative variation for these traits and apply this information for crop improvement programs.

Identification of tomato root growth regulatory genes and transcription factors through comparative transcriptomic profiling of different tissues

Tomato is an economically important vegetable crop and a model for development and stress response studies. Although studied extensively for understanding fruit ripening and pathogen responses, its role as a model for root development remains less explored. In this study, an Illumina-based comparative differential transcriptomic analysis of tomato root with different aerial tissues was carried out to identify genes that are predominantly expressed during root growth. Sequential comparisons revealed ~ 15,000 commonly expressed genes and ~ 3000 genes of several classes that were mainly expressed or regulated in roots. These included 1069 transcription factors (TFs) of which 100 were differentially regulated. Prominent amongst these were members of families encoding Zn finger, MYB, ARM, bHLH, AP2/ERF, WRKY and NAC proteins. A large number of kinases, phosphatases and F-box proteins were also expressed in the root transcriptome. The major hormones regulating root growth were represented by the auxin, ethylene, JA, ABA and GA pathways with root-specific expression of certain components. Genes encoding carbon metabolism and photosynthetic components showed reduced expression while several protease inhibitors were amongst the most highly expressed. Overall, the study sheds light on genes governing root growth in tomato and provides a resource for manipulation of root growth for plant improvement.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01015-0.

Deciphering the genetic basis of root morphology, nutrient uptake, yield, and yield-related traits in rice under dry direct-seeded cultivation systems

In the face of global water scarcity, a successful transition of rice cultivation from puddled to dry direct-seeded rice (DDSR) is a future need. A genome-wide association study was performed on a complex mapping population for 39 traits: 9 seedling-establishment traits, 14 root and nutrient-uptake traits, 5 plant morphological traits, 4 lodging resistance traits, and 7 yield and yield-contributing traits. A total of 10 significant marker-trait associations (MTAs) were found along with 25 QTLs associated with 25 traits. The percent phenotypic variance explained by SNPs ranged from 8% to 84%. Grain yield was found to be significantly and positively correlated with seedling-establishment traits, root morphological traits, nutrient uptake-related traits, and grain yield-contributing traits. The genomic colocation of different root morphological traits, nutrient uptake-related traits, and grain-yield-contributing traits further supports the role of root morphological traits in improving nutrient uptake and grain yield under DDSR. The QTLs/candidate genes underlying the significant MTAs were identified. The identified promising progenies carrying these QTLs may serve as potential donors to be exploited in genomics-assisted breeding programs for improving grain yield and adaptability under DDSR.

Drought and heat stress-related proteins: an update about their functional relevance in imparting stress tolerance in agricultural crops

We describe here the recent developments about the involvement of diverse stress-related proteins in sensing, signaling, and defending the cells in plants in response to drought or/and heat stress. In the current era of global climate drift, plant growth and productivity are often limited by various environmental stresses, especially drought and heat. Adaptation to abiotic stress is a multigenic process involving maintenance of homeostasis for proper survival under adverse environment. It has been widely observed that a series of proteins respond to heat and drought conditions at both transcriptional and translational levels. The proteins are involved in various signaling events, act as key transcriptional activators and saviors of plants under extreme environments. A detailed insight about the functional aspects of diverse stress-responsive proteins may assist in unraveling various stress resilience mechanisms in plants. Furthermore, by identifying the metabolic proteins associated with drought and heat tolerance, tolerant varieties can be produced through transgenic/recombinant technologies. A large number of regulatory and functional stress-associated proteins are reported to participate in response to heat and drought stresses, such as protein kinases, phosphatases, transcription factors, and late embryogenesis abundant proteins, dehydrins, osmotins, and heat shock proteins, which may be similar or unique to stress treatments. Few studies have revealed that cellular response to combined drought and heat stresses is distinctive, compared to their individual treatments. In this review, we would mainly focus on the new developments about various stress sensors and receptors, transcription factors, chaperones, and stress-associated proteins involved in drought or/and heat stresses, and their possible role in augmenting stress tolerance in crops.

Meta-analysis of drought-tolerant genotypes in Oryza sativa: A network-based approach

BACKGROUND

Drought is a severe environmental stress. It is estimated that about 50% of the world rice production is affected mainly by drought. Apart from conventional breeding strategies to develop drought-tolerant crops, innovative computational approaches may provide insights into the underlying molecular mechanisms of stress response and identify drought-responsive markers. Here we propose a network-based computational approach involving a meta-analytic study of seven drought-tolerant rice genotypes under drought stress.

RESULTS

Co-expression networks enable large-scale analysis of gene-pair associations and tightly coupled clusters that may represent coordinated biological processes. Considering differentially expressed genes in the co-expressed modules and supplementing external information such as resistance/tolerance QTLs, transcription factors, network-based topological measures, we identify and prioritize drought-adaptive co-expressed gene modules and potential candidate genes. Using the candidate genes that are well-represented across the datasets as 'seed' genes, two drought-specific protein-protein interaction networks (PPINs) are constructed with up- and down-regulated genes. Cluster analysis of the up-regulated PPIN revealed ABA signalling pathway as a central process in drought response with a probable crosstalk with energy metabolic processes. Tightly coupled gene clusters representing up-regulation of core cellular respiratory processes and enhanced degradation of branched chain amino acids and cell wall metabolism are identified. Cluster analysis of down-regulated PPIN provides a snapshot of major processes associated with photosynthesis, growth, development and protein synthesis, most of which are shut down during drought. Differential regulation of phytohormones, e.g., jasmonic acid, cell wall metabolism, signalling and posttranslational modifications associated with biotic stress are elucidated. Functional characterization of topologically important, drought-responsive uncharacterized genes that may play a role in important processes such as ABA signalling, calcium signalling, photosynthesis and cell wall metabolism is discussed. Further transgenic studies on these genes may help in elucidating their biological role under stress conditions.

CONCLUSION

Currently, a large number of resources for rice functional genomics exist which are mostly underutilized by the scientific community. In this study, a computational approach integrating information from various resources such as gene co-expression networks, protein-protein interactions and pathway-level information is proposed to provide a systems-level view of complex drought-responsive processes across the drought-tolerant genotypes.

Molecular Mechanisms of Root Development in Rice

Roots are fundamentally important for growth and development, anchoring the plant to its growth substrate, facilitating water and nutrient uptake from the soil, and sensing and responding to environmental signals such as biotic and abiotic stresses. Understanding the molecular mechanisms controlling root architecture is essential for improving nutrient uptake efficiency and crop yields. In this review, we describe the progress being made in the identification of genes and regulatory pathways involved in the development of root systems in rice (Oryza sativa L.), including crown roots, lateral roots, root hairs, and root length. Genes involved in the adaptation of roots to the environmental nutrient status are reviewed, and strategies for further study and agricultural applications are discussed. The growth and development of rice roots are controlled by both genetic factors and environmental cues. Plant hormones, especially auxin and cytokinin, play important roles in root growth and development. Understanding the molecular mechanisms regulating root architecture and response to environmental signals can contribute to the genetic improvement of crop root systems, enhancing their adaptation to stressful environmental conditions.

Genome-wide characterization, evolution, and expression analysis of the leucine-rich repeat receptor-like protein kinase (LRR-RLK) gene family in Rosaceae genomes

BACKGROUND

Leucine-rich repeat receptor-like protein kinase (LRR-RLK) is the largest gene family of receptor-like protein kinases (RLKs) and actively participates in regulating the growth, development, signal transduction, immunity, and stress responses of plants. However, the patterns of LRR-RLK gene family evolution in the five main Rosaceae species for which genome sequences are available have not yet been reported. In this study, we performed a comprehensive analysis of LRR-RLK genes for five Rosaceae species: Fragaria vesca (strawberry), Malus domestica (apple), Pyrus bretschneideri (Chinese white pear), Prunus mume (mei), and Prunus persica (peach), which contained 201, 244, 427, 267, and 258 LRR-RLK genes, respectively.

RESULTS

All LRR-RLK genes were further grouped into 23 subfamilies based on the hidden Markov models approach. RLK-Pelle_LRR-XII-1, RLK-Pelle_LRR-XI-1, and RLK-Pelle_LRR-III were the three largest subfamilies. Synteny analysis indicated that there were 236 tandem duplicated genes in the five Rosaceae species, among which subfamilies XII-1 (82 genes) and XI-1 (80 genes) comprised 68.6%.

CONCLUSIONS

Our results indicate that tandem duplication made a large contribution to the expansion of the subfamilies. The gene expression, tissue-specific expression, and subcellular localization data revealed that LRR-RLK genes were differentially expressed in various organs and tissues, and the largest subfamily XI-1 was highly expressed in all five Rosaceae species, suggesting that LRR-RLKs play important roles in each stage of plant growth and development. Taken together, our results provide an overview of the LRR-RLK family in Rosaceae genomes and the basis for further functional studies.

The role of receptor-like protein kinases (RLKs) in abiotic stress response in plants

We review and introduce recent studies on RLK s involved in the abiotic stress response and provide insights into potential regulatory mechanisms for alleviating abiotic stress. Abiotic stresses are important factors affecting plant growth and development, resulting in crop production reduction and even plant death. To survive, plants utilize different mechanisms to respond and adapt to continuously changing environmental factors. Understanding of the molecular mechanisms of plant response to various stresses will aid in improving tolerance of plants to abiotic stress through genetic engineering, which would greatly promote the development of modern agriculture. RLKs, the largest gene family in plants, play critical roles in the regulation of plant developmental processes, signaling networks and disease resistance. Many RLKs have been shown to be involved in abiotic stress responses, including the abscisic acid response, calcium signaling and antioxidant defense. This review summarizes recent studies on RLKs involved in plant responses to abiotic stress, including drought, salt, cold, toxic metals/metalloids and other stresses, and emphasizes the upstream and downstream factors in RLK signal transduction pathways under abiotic stress.

Updated Rice Kinase Database RKD 2.0: enabling transcriptome and functional analysis of rice kinase genes

BACKGROUND

Protein kinases catalyze the transfer of a phosphate moiety from a phosphate donor to the substrate molecule, thus playing critical roles in cell signaling and metabolism. Although plant genomes contain more than 1000 genes that encode kinases, knowledge is limited about the function of each of these kinases. A major obstacle that hinders progress towards kinase characterization is functional redundancy. To address this challenge, we previously developed the rice kinase database (RKD) that integrated omics-scale data within a phylogenetics context.

RESULTS

An updated version of rice kinase database (RKD) that contains metadata derived from NCBI GEO expression datasets has been developed. RKD 2.0 facilitates in-depth transcriptomic analyses of kinase-encoding genes in diverse rice tissues and in response to biotic and abiotic stresses and hormone treatments. We identified 261 kinases specifically expressed in particular tissues, 130 that are significantly up- regulated in response to biotic stress, 296 in response to abiotic stress, and 260 in response to hormones. Based on this update and Pearson correlation coefficient (PCC) analysis, we estimated that 19 out of 26 genes characterized through loss-of-function studies confer dominant functions. These were selected because they either had paralogous members with PCC values of <0.5 or had no paralog.

CONCLUSION

Compared with the previous version of RKD, RKD 2.0 enables more effective estimations of functional redundancy or dominance because it uses comprehensive expression profiles rather than individual profiles. The integrated analysis of RKD with PCC establishes a single platform for researchers to select rice kinases for functional analyses.

Ectopic expression of TAPETUM DETERMINANT1 affects ovule development in Arabidopsis

Plants have evolved to extensively employ leucine-rich repeat receptor-like kinases (LRR-RLKs), the largest family of RLKs, to control growth, development, and defense. In Arabidopsis thaliana, the EXCESS MICROSPOROCYTES1 (EMS1) LRR-RLK and its potential small protein ligand TAPETUM DETERMINANT1 (TPD1) are specifically required for anther cell differentiation; however, TPD1 and EMS1 orthologs also control megaspore mother cell proliferation in rice and maize ovules. Here, the molecular function of TPD1 was demonstrated during ovule development in Arabidopsis using a gain-of-function approach. In ovules, the EMS1 gene was primarily expressed in nucellus epidermis and chalaza, whereas the expression of TPD1 was weakly restricted to the distal end of integuments. Ectopic expression of TPD1 caused pleiotropic defects in ovule and seed development. RNA sequencing analysis showed that ectopic expression of TPD1 altered expression of auxin signaling genes and core cell-cycle genes during ovule development. Moreover, ectopic expression of TPD1 not only affected auxin response but also enhanced expression of cyclin genes CYCD3;3 and CYCA2;3 in ovules. Thus, these results provide insight into the molecular mechanism by which TPD1-EMS1 signaling controls plant development possibly via regulation of auxin signaling and cell-cycle genes.

The phenome analysis of mutant alleles in Leucine-Rich Repeat Receptor-Like Kinase genes in rice reveals new potential targets for stress tolerant cereals

Plants are constantly exposed to a variety of biotic and abiotic stresses that reduce their fitness and performance. At the molecular level, the perception of extracellular stimuli and the subsequent activation of defense responses require a complex interplay of signaling cascades, in which protein phosphorylation plays a central role. Several studies have shown that some members of the Leucine-Rich Repeat Receptor-Like Kinase (LRR-RLK) family are involved in stress and developmental pathways. We report here a systematic analysis of the role of the members of this gene family by mutant phenotyping in the monocotyledon model plant rice, Oryza sativa. We have then targeted 176 of the ∼320 LRR-RLK genes (55.7%) and genotyped 288 mutant lines. Position of the insertion was confirmed in 128 lines corresponding to 100 LRR-RLK genes (31.6% of the entire family). All mutant lines harboring homozygous insertions have been screened for phenotypes under normal conditions and under various abiotic stresses. Mutant plants have been observed at several stages of growth, from seedlings in Petri dishes to flowering and grain filling under greenhouse conditions. Our results show that 37 of the LRR-RLK rice genes are potential targets for improvement especially in the generation of abiotic stress tolerant cereals.

Plant development regulation: Overview and perspectives

Plant development, as occur in other eukaryotes, is conducted through a complex network of hormones, transcription factors, enzymes and micro RNAs, among other cellular components. They control developmental processes such as embryo, apical root and shoot meristem, leaf, flower, or seed formation, among others. The research in these topics has been very active in last decades. Recently, an explosion of new data concerning regulation mechanisms as well as the response of these processes to environmental changes has emerged. Initially, most of investigations were carried out in the model eudicot Arabidopsis but currently data from other plant species are available in the literature, although they are still limited. The aim of this review is focused on summarize the main molecular actors involved in plant development regulation in diverse plant species. A special attention will be given to the major families of genes and proteins participating in these regulatory mechanisms. The information on the regulatory pathways where they participate will be briefly cited. Additionally, the importance of certain structural features of such proteins that confer ductility and flexibility to these mechanisms will also be reported and discussed.

Challenges of modifying root traits in crops for agriculture

Roots play an essential role in the acquisition of water and minerals from soils. Measuring crop root architecture and assaying for changes in function can be challenging, but examples have emerged showing that modifications to roots result in higher yield and increased stress tolerance. In this review, we focus mainly on the molecular genetic advances that have been made in altering root system architecture and function in crop plants, as well as phenotyping methods. The future for the modification of crop plant roots looks promising based on recent advances, but there are also important challenges ahead.

Novel ABP1-TMK auxin sensing system controls ROP GTPase-mediated interdigitated cell expansion in Arabidopsis

ROP GTPases (Rho-like GTPase from plants), plant counterparts of animal and fungal Rho-family GTPases, have recently been shown to be key components of a novel signaling pathway activated by the plant hormone auxin. Auxin (indole acetic acid) is a key regulator of virtually every aspect of plant growth and development, yet the molecular mechanisms of auxin responses remain largely unknown. AUXIN BINDING PROTEIN1 (ABP1) is an ancient protein that binds auxin and has been implied as a receptor for a number of auxin responses, but its precise mechanism remains unresolved. A paradox for ABP1's action is that it is predominantly found in the endoplasmic reticulum (ER) lumen, while it has been implicated as a cell surface auxin receptor, functionally distinct from the nuclear TIR1/AFB auxin receptor family that regulates transcriptional responses. Since our group reported that ABP1 is required for activating two antagonizing ROP signaling pathways involved in cytoskeletal reorganization and cell shape formation in Arabidopsis leaf pavement cells, we recently further showed that the plasma membrane-localized TMK receptor-like kinases functionally interact in a complex with ABP1 and are required for ABP1-dependent activation of ROP GTPases by auxin. The formation of this cell surface complex is induced by auxin and requires functional ABP1. These exciting findings provide convincing evidence for this novel auxin sensing system on the cell surface and suggest intriguing mechanisms for TMKs being functional partners of ABP1 to transmit extracellular auxin signal to intracellular ROP signaling module during polar cell expansion.