Arabinogalactan proteins (AGPs) are structurally complex plasma membrane and cell wall proteoglycans that are implicated in diverse developmental processes, including plant sexual reproduction. Male gametogenesis (pollen grain development) is fundamental to plant sexual reproduction. The role of two abundant, pollen-specific AGPs, AGP6, and AGP11, have been investigated here. The pollen specificity of these proteoglycans suggested that they are integral to pollen biogenesis and their strong sequence homology indicated a potential for overlapping function. Indeed, single gene transposon insertion knockouts for both AGPs showed no discernible phenotype. However, in plants homozygous for one of the insertions and heterozygous for the other, in homozygous double mutants, and in RNAi and amiRNA transgenic plants that were down-regulated for both genes, many pollen grains failed to develop normally, leading to their collapse. The microscopic observations of these aborted pollen grains showed a condensed cytoplasm, membrane blebbing and the presence of small lytic vacuoles. Later in development, the generative cells that arise from mitotic divisions were not seen to go into the second mitosis. Anther wall development, the establishment of the endothecium thickenings, the opening of the stomium, and the deposition of the pollen coat were all normal in the knockout and knockdown lines. Our data provide strong evidence that these two proteoglycans have overlapping and important functions in gametophytic pollen grain development.

Successful plant reproduction relies on the perfect orchestration of singular processes that culminate in the product of reproduction: the seed. The floral transition, floral organ development, and fertilization are well-studied processes and the genetic regulation of the various steps is being increasingly unveiled. Initially, based predominantly on genetic studies, the regulatory pathways were considered to be linear, but recent genome-wide analyses, using high-throughput technologies, have begun to reveal a different scenario. Complex gene regulatory networks underlie these processes, including transcription factors, microRNAs, movable factors, hormones, and chromatin-modifying proteins. Here we review recent progress in understanding the networks that control the major steps in plant reproduction, showing how new advances in experimental and computational technologies have been instrumental. As these recent discoveries were obtained using the model species Arabidopsis thaliana, we will restrict this review to regulatory networks in this important model species. However, more fragmentary information obtained from other species reveals that both the developmental processes and the underlying regulatory networks are largely conserved, making this review also of interest to those studying other plant species.

Background and Aims The REM (Reproductive Meristem) gene family of Arabidopsis thaliana is part of the B3 DNA-binding domain superfamily. Despite the fact that several groups have worked on the REM genes for many years, little is known about the function of this transcription factor family. This study aims to identify a set of REM genes involved in flower development and to characterize their function. Methods In order to provide an overview of the REM gene family, a detailed expression analysis for all REM genes of A. thaliana was performed and combined with a meta-analysis of ChIP-sequencing and microarray experiments. Key Results Two sets of phylogenetically closely related REM genes, namely REM23, REM24 and REM25, and REM34, REM35 and REM36, were identified as possibly being involved in the early stages of flower development. Single- and double-mutant combinations were analysed for these genes, and no phenotypic effects were detected during flower development. Conclusions The data suggest that the REM34, REM35 and REM36 group is the most interesting one, as REM34 is co-expressed with the floral meristem identity (FMI) genes, they are bound by AP1, SVP, AP3 and PI, and they are expressed in the floral meristem and during the earliest stages of flower development. However, it appears that high levels of functional redundancy may conceal the exact function of these transcription factor genes.

MADS domain transcription factors are key regulators of eukaryotic development. In plants, the homeotic MIKC MADS factors that regulate floral organ identity have been studied in great detail. Based on genetic and protein–protein interaction studies, a floral quartet model was proposed that describes how these MADS domain proteins assemble into higher order complexes to regulate their target genes. However, despite the attractiveness of this model and its general acceptance in the literature, solid in vivo proof has never been provided. To gain deeper insight into the mechanisms of transcriptional regulation by MADS domain factors, we studied how SEEDSTICK (STK) and SEPALLATA3 (SEP3) directly regulate the expression of the reproductive meristem gene family transcription factor–encoding gene VERDANDI (VDD). Our data show that STK-SEP3 dimers can induce loop formation in the VDD promoter by binding to two nearby CC(A/T)6GG (CArG) boxes and that this is essential for promoter activity. Our in vivo data show that the size and position of this loop, determined by the choice of CArG element usage, is essential for correct expression. Our studies provide solid in vivo evidence for the floral quartet model.

The increment in global temperature reduces crop productivity, which in turn threatens food security. Currently, most of our food supply is produced by plants and the human population is estimated to reach 9 billion by 2050. Gaining insights into how plants navigate heat stress in their reproductive phase is essential for effectively overseeing the future of agricultural productivity. The reproductive success of numerous plant species can be jeopardized by just one exceptionally hot day. While the effects of heat stress on seedlings germination and root development have been extensively investigated, studies on reproduction are limited. The intricate processes of gamete development and fertilization unfold within a brief timeframe, largely concealed within the flower. Nonetheless, heat stress is known to have important effects on reproduction. Considering that heat stress typically affects both male and female reproductive structures concurrently, it remains crucial to identify cultivars with thermotolerance. In such cultivars, ovules and pollen can successfully undergo development despite the challenges posed by heat stress, enabling the completion of the fertilization process and resulting in a robust seed yield. Hereby, we review the current understanding of the molecular mechanisms underlying plant resistance to abiotic heat stress, focusing on the reproductive process in the model systems of Arabidopsis and Oryza sativa.