Evolutionary history of the grass gynoecium

Morpho Evo-Devo of the Gynoecium: Heterotopy, Redefinition of the Carpel, and a Topographic Approach

Since the 19th century, we have had countless debates, sometimes acrimonious, about the nature of the gynoecium. A pivotal question has been whether all angiosperms possess carpels or if some or all angiosperms are acarpellate. We can resolve these debates if we do not define the carpel as a closed megasporophyll but simply as an appendage that encloses the placenta or a single ovule. This redefinition may, however, lead to confusion because often it may not be clear whether the traditional (classical) definition of the carpel or the redefinition is implied. Therefore, a topographic approach is proposed that is compatible with the redefinition. According to this approach, gynoecia comprise one or more gynoecial appendages and placentas or single ovules that may be formed in different positions. Heterotopy refers to these different positions. In the context of evo-devo, which explores evolutionary changes in development, morpho evo-devo delves into spatial shifts of the placentas and ovules leading to heterotopy. Furthermore, it considers shifts in timing (heterochrony) and other processes leading to heteromorphy. Recognizing spatial shifting of the placentas or a single ovule and other evolutionary processes opens up new vistas in the search for the ancestor(s) of angiosperms and their gynoecia.

Basic helix-loop-helix (bHLH) gene family in rye (Secale cereale L.): genome-wide identification, phylogeny, evolutionary expansion and expression analyses

BACKGROUND

Rye (Secale cereale), one of the drought and cold-tolerant crops, is an important component of the Triticae Dumortier family of Gramineae plants. Basic helix-loop-helix (bHLH), an important family of transcription factors, has played pivotal roles in regulating numerous intriguing biological processes in plant development and abiotic stress responses. However, no systemic analysis of the bHLH transcription factor family has yet been reported in rye.

RESULTS

In this study, 220 bHLH genes in S. cereale (ScbHLHs) were identified and named based on the chromosomal location. The evolutionary relationships, classifications, gene structures, motif compositions, chromosome localization, and gene replication events in these ScbHLH genes are systematically analyzed. These 220 ScbHLH members are divided into 21 subfamilies and one unclassified gene. Throughout evolution, the subfamilies 5, 9, and 18 may have experienced stronger expansion. The segmental duplications may have contributed significantly to the expansion of the bHLH family. To systematically analyze the evolutionary relationships of the bHLH family in different plants, we constructed six comparative genomic maps of homologous genes between rye and different representative monocotyledonous and dicotyledonous plants. Finally, the gene expression response characteristics of 22 ScbHLH genes in various biological processes and stress responses were analyzed. Some candidate genes, such as ScbHLH11, ScbHLH48, and ScbHLH172, related to tissue developments and environmental stresses were screened.

CONCLUSIONS

The results indicate that these ScbHLH genes exhibit characteristic expression in different tissues, grain development stages, and stress treatments. These findings provided a basis for a comprehensive understanding of the bHLH family in rye.

Patterns of Carpel Structure, Development, and Evolution in Monocots

The phenomenon of heterochrony, or shifts in the relative timing of ontogenetic events, is important for understanding many aspects of plant evolution, including applied issues such as crop yield. In this paper, we review heterochronic shifts in the evolution of an important floral organ, the carpel. The carpels, being ovule-bearing organs, facilitate fertilisation, seed, and fruit formation. It is the carpel that provides the key character of flowering plants, angiospermy. In many angiosperms, a carpel has two zones: proximal ascidiate and distal plicate. When carpels are free (apocarpous gynoecium), the plicate zone has a ventral slit where carpel margins meet and fuse during ontogeny; the ascidiate zone is sac-like from inception and has no ventral slit. When carpels are united in a syncarpous gynoecium, a synascidiate zone has as many locules as carpels, whereas a symplicate zone is unilocular, at least early in ontogeny. In ontogeny, either the (syn)ascidiate or (sym)plicate zone is first to initiate. The two developmental patterns are called early and late peltation, respectively. In extreme cases, either the (sym)plicate or (syn)ascidiate zone is completely lacking. Here, we discuss the diversity of carpel structure and development in a well-defined clade of angiosperms, the monocotyledons. We conclude that the common ancestor of monocots had carpels with both zones and late peltation. This result was found irrespective of the use of the plastid or nuclear phylogeny. Early peltation generally correlates with ovules belonging to the (syn)ascidiate zone, whereas late peltation is found mostly in monocots with a fertile (sym)plicate zone.

Flower heterochrony and crop yield

Crop improvement has focused on enhancing yield, nutrient content, harvestability, and stress resistance using a trait-centered reductionist approach. This has downplayed the fact that plants are developmentally integrated and respond coordinately and predictably to genetic and environmental variation, with potential consequences for food production. Crop yield, including both fruit/seed production and the possibility of generating hybrid crop varieties, is highly dependent on flower morphology and sex, which, in turn, can be profoundly affected by slight shifts in the timing and rate of flower organ development (i.e., flower heterochrony). We argue that understanding the genetic and environmental bases of flower heterochrony and their effect on flower morphology and sex in cultivated plants and in their wild relatives can facilitate crop improvement.

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.