Competitive Ability of Maize Pollen Grains Requires Paralogous Serine Threonine Protein Kinases STK1 and STK2

Research Progress on Gene Regulation of Plant Floral Organogenesis

Flowers, serving as the reproductive structures of angiosperms, perform an integral role in plant biology and are fundamental to understanding plant evolution and taxonomy. The growth and organogenesis of flowers are driven by numerous factors, such as external environmental conditions and internal physiological processes, resulting in diverse traits across species or even within the same species. Among these factors, genes play a central role, governing the entire developmental process. The regulation of floral genesis by these genes has become a significant focus of research. In the AE model of floral development, the five structural whorls (calyx, corolla, stamens, pistils, and ovules) are controlled by five groups of genes: A, B, C, D, and E. These genes interact to give rise to a complex control system that governs the floral organsgenesis. The activation or suppression of specific gene categories results in structural modifications to floral organs, with variations observed across different species. The present article examines the regulatory roles of key genes, including genes within the MADS-box and AP2/ERF gene clusters, such as AP1, AP2, AP3, AG, STK, SHP, SEP, PI, and AGL6, as well as other genes, like NAP, SPL, TGA, PAN, and WOX, in shaping floral organ genesis. In addition, it analyzes the molecular-level effects of these genes on floral organ formation. The findings offer a deeper understanding of the genetic governance of floral organ genesis across plant species.

The triticale mature pollen and stigma proteomes - assembling the proteins for a productive encounter

Triticeae crops are major contributors to global food production and ensuring their capacity to reproduce and generate seeds is critical. However, despite their importance our knowledge of the proteins underlying Triticeae reproduction is severely lacking and this is not only true of pollen and stigma development, but also of their pivotal interaction. When the pollen grain and stigma are brought together they have each accumulated the proteins required for their intended meeting and accordingly studying their mature proteomes is bound to reveal proteins involved in their diverse and complex interactions. Using triticale as a Triticeae representative, gel-free shotgun proteomics was used to identify 11,533 and 2977 mature stigma and pollen proteins respectively. These datasets, by far the largest to date, provide unprecedented insights into the proteins participating in Triticeae pollen and stigma development and interactions. The study of the Triticeae stigma has been particularly neglected. To begin filling this knowledge gap, a developmental iTRAQ analysis was performed revealing 647 proteins displaying differential abundance as the stigma matures in preparation for pollination. An in-depth comparison to an equivalent Brassicaceae analysis divulged both conservation and diversification in the makeup and function of proteins involved in the pollen and stigma encounter. SIGNIFICANCE: Successful pollination brings together the mature pollen and stigma thus initiating an intricate series of molecular processes vital to crop reproduction. In the Triticeae crops (e.g. wheat, barley, rye, triticale) there persists a vast deficit in our knowledge of the proteins involved which needs to be addressed if we are to face the many upcoming challenges to crop production such as those associated with climate change. At maturity, both the pollen and stigma have acquired the protein complement necessary for their forthcoming encounter and investigating their proteomes will inevitably provide unprecedented insights into the proteins enabling their interactions. By combining the analysis of the most comprehensive Triticeae pollen and stigma global proteome datasets to date with developmental iTRAQ investigations, proteins implicated in the different phases of pollen-stigma interaction enabling pollen adhesion, recognition, hydration, germination and tube growth, as well as those underlying stigma development were revealed. Extensive comparisons between equivalent Triticeae and Brassiceae datasets highlighted both the conservation of biological processes in line with the shared goal of activating the pollen grain and promoting pollen tube invasion of the pistil to effect fertilization, as well as the significant distinctions in their proteomes consistent with the considerable differences in their biochemistry, physiology and morphology.

A cost-effective maize ear phenotyping platform enables rapid categorization and quantification of kernels

High-throughput phenotyping systems are powerful, dramatically changing our ability to document, measure, and detect biological phenomena. Here, we describe a cost-effective combination of a custom-built imaging platform and deep-learning-based computer vision pipeline. A minimal version of the maize (Zea mays) ear scanner was built with low-cost and readily available parts. The scanner rotates a maize ear while a digital camera captures a video of the surface of the ear, which is then digitally flattened into a two-dimensional projection. Segregating GFP and anthocyanin kernel phenotypes are clearly distinguishable in ear projections and can be manually annotated and analyzed using image analysis software. Increased throughput was attained by designing and implementing an automated kernel counting system using transfer learning and a deep learning object detection model. The computer vision model was able to rapidly assess over 390 000 kernels, identifying male-specific transmission defects across a wide range of GFP-marked mutant alleles. This includes a previously undescribed defect putatively associated with mutation of Zm00001d002824, a gene predicted to encode a vacuolar processing enzyme. Thus, by using this system, the quantification of transmission data and other ear and kernel phenotypes can be accelerated and scaled to generate large datasets for robust analyses.

A cost-effective maize ear phenotyping platform enables rapid categorization and quantification of kernels

High-throughput phenotyping systems are powerful, dramatically changing our ability to document, measure, and detect biological phenomena. Here, we describe a cost-effective combination of a custom-built imaging platform and deep-learning-based computer vision pipeline. A minimal version of the maize (Zea mays) ear scanner was built with low-cost and readily available parts. The scanner rotates a maize ear while a digital camera captures a video of the surface of the ear, which is then digitally flattened into a two-dimensional projection. Segregating GFP and anthocyanin kernel phenotypes are clearly distinguishable in ear projections and can be manually annotated and analyzed using image analysis software. Increased throughput was attained by designing and implementing an automated kernel counting system using transfer learning and a deep learning object detection model. The computer vision model was able to rapidly assess over 390 000 kernels, identifying male-specific transmission defects across a wide range of GFP-marked mutant alleles. This includes a previously undescribed defect putatively associated with mutation of Zm00001d002824, a gene predicted to encode a vacuolar processing enzyme. Thus, by using this system, the quantification of transmission data and other ear and kernel phenotypes can be accelerated and scaled to generate large datasets for robust analyses.

A Maize Male Gametophyte-Specific Gene Encodes ZmLARP6c1, a Potential RNA-Binding Protein Required for Competitive Pollen Tube Growth

Members of the La-related protein family (LARPs) contain a conserved La module, which has been associated with RNA-binding activity. Expression of the maize gene GRMZM2G323499/Zm00001d018613, a member of the LARP family, is highly specific to pollen, based on both transcriptomic and proteomic assays. This suggests a pollen-specific RNA regulatory function for the protein, designated ZmLARP6c1 based on sequence similarity to the LARP6 subfamily in Arabidopsis. To test this hypothesis, a Ds-GFP transposable element insertion in the ZmLarp6c1 gene (tdsgR82C05) was obtained from the Dooner/Du mutant collection. Sequencing confirmed that the Ds-GFP insertion is in an exon, and thus likely interferes with ZmLARP6c1 function. Tracking inheritance of the insertion via its endosperm-expressed GFP indicated that the mutation was associated with reduced transmission from a heterozygous plant when crossed as a male (ranging from 0.5 to 26.5% transmission), but not as a female. Furthermore, this transmission defect was significantly alleviated when less pollen was applied to the silk, reducing competition between mutant and wild-type pollen. Pollen grain diameter measurements and nuclei counts showed no significant differences between wild-type and mutant pollen. However, in vitro, mutant pollen tubes were significantly shorter than those from sibling wild-type plants, and also displayed altered germination dynamics. These results are consistent with the idea that ZmLARP6c1 provides an important regulatory function during the highly competitive progamic phase of male gametophyte development following arrival of the pollen grain on the silk. The conditional, competitive nature of the Zmlarp6c1::Ds male sterility phenotype (i.e., reduced ability to produce progeny seed) points toward new possibilities for genetic control of parentage in crop production.

Phylogeny, structural diversity and genome-wide expression analysis of fibrillin family genes in rice

Fibrillins (FBNs) constitute a plastid-lipid-associated protein family that plays a role in chloroplast development, lipids metabolism and stress responses in plants. Until now, FBNs have been functionally characterized in stability of thylakoid and responses to the different stress stimuli. Consequently, phylogeny, domain composition and structural features of 121 FBNs family proteins from ten representative species have been identified. As results, phylogenetic analysis demonstrated that FBNs proteins were grouped into 24 clades and further subdivided into three groups, including terrestrial plant-specific, algae-specific, and intermediate group. These FBNs genes had different numbers of introns and exons but encoded the conserved N-terminal chloroplast transport peptide (CTP) domains and plastid lipid-associated protein (PAP) domains, which greatly contributed to the sub-functionalization and neo-functionalization. Meanwhile, the CTP domains of eleven OsFBN proteins except OsFBN8 could help them transport into chloroplasts. The PAP domains of OsFBN2 and OsFBN4 showed the in vitro specific binding activity to C12-C22 fatty acids that were affected by YxD motif. The qRT-PCR analysis showed that OsFBN genes were differentially induced by heat stress and cold stress in rice. Collectively, this study has provided the new insights into the evolution, structure, and functions of FBN gene family and will help to elucidate the molecular mechanisms of these proteins functioning in growth, development and adaptations in the global climate change.

High expression in maize pollen correlates with genetic contributions to pollen fitness as well as with coordinated transcription from neighboring transposable elements

In flowering plants, gene expression in the haploid male gametophyte (pollen) is essential for sperm delivery and double fertilization. Pollen also undergoes dynamic epigenetic regulation of expression from transposable elements (TEs), but how this process interacts with gene expression is not clearly understood. To explore relationships among these processes, we quantified transcript levels in four male reproductive stages of maize (tassel primordia, microspores, mature pollen, and sperm cells) via RNA-seq. We found that, in contrast with vegetative cell-limited TE expression in Arabidopsis pollen, TE transcripts in maize accumulate as early as the microspore stage and are also present in sperm cells. Intriguingly, coordinate expression was observed between highly expressed protein-coding genes and their neighboring TEs, specifically in mature pollen and sperm cells. To investigate a potential relationship between elevated gene transcript level and pollen function, we measured the fitness cost (male-specific transmission defect) of GFP-tagged coding sequence insertion mutations in over 50 genes identified as highly expressed in the pollen vegetative cell, sperm cell, or seedling (as a sporophytic control). Insertions in seedling genes or sperm cell genes (with one exception) exhibited no difference from the expected 1:1 transmission ratio. In contrast, insertions in over 20% of vegetative cell genes were associated with significant reductions in fitness, showing a positive correlation of transcript level with non-Mendelian segregation when mutant. Insertions in maize gamete expressed2 (Zm gex2), the sole sperm cell gene with measured contributions to fitness, also triggered seed defects when crossed as a male, indicating a conserved role in double fertilization, given the similar phenotype previously demonstrated for the Arabidopsis ortholog GEX2. Overall, our study demonstrates a developmentally programmed and coordinated transcriptional activation of TEs and genes in pollen, and further identifies maize pollen as a model in which transcriptomic data have predictive value for quantitative phenotypes.

ZmSTK1 and ZmSTK2, encoding receptor-like cytoplasmic kinase, are involved in maize pollen development with additive effect

Pollen germination and pollen tube growth are important physiological processes of sexual reproduction of plants and also are involved in signal transduction. Our previous study reveals that ZmSTK1 and ZmSTK2 are two receptor-like cytoplasmic kinases (RLCK) homologs in Zea mays as members of receptor-like protein kinase (RLK) subfamily, sharing 86% identity at the amino acid level. Here, we report that ZmSTK1 and ZmSTK2, expressed at late stages of pollen development, regulate maize pollen development with additive effect. ZmSTK1 or ZmSTK2 mutation exhibited severe pollen transmission deficiency, which thus influenced pollen fertility. Moreover, the kinase domains of ZmSTKs were cross-interacted with C-terminus of enolases detected by co-immunoprecipitation (Co-IP) and yeast two-hybrid system (Y2H), respectively. Further, the detective ZmSTK1 or ZmSTK2 was associated with decreased activity of enolases and also reduced downstream metabolite contents, which enolases are involved in glycolytic pathway, such as phosphoenolpyruvate (PEP), pyruvate, ADP/ATP, starch, glucose, sucrose and fructose. This study reveals that ZmSTK1 and ZmSTK2 regulate maize pollen development and indirectly participate in glycolytic pathway.