GhGPAT12/25 Are Essential for the Formation of Anther Cuticle and Pollen Exine in Cotton (Gossypium hirsutum L.)

Glycerol-3-phosphate acyltransferases (GPATs), critical for multiple biological processes like male fertility, have been extensively characterized. However, their precise functions and underlying regulatory mechanism in cotton anther development are unclear. This research demonstrated the importance of GhGPAT12/25 (a paralogs pair on A12/D12 sub-chromosome of cotton) to regulate the degradation of tapetum, anther cuticle formation, and pollen exine development. GhGPAT12 and GhGPAT25 exhibited specifically detected transcripts in tapetum and pollen exine during the early anther developmental stages. GhGPAT12/25 are sn-2 glycerol-3-phosphate acyltransferases and can transfer the acyl group of palmitoyl-CoA to glycerol-3-phosphate (G3P). CRISPR/Cas9-mediated knockout identified the functional redundancy of GhGPAT12 and GhGPAT25. Knockout of both genes caused completely male sterility associated with abnormal anther cuticle, swollen tapetum, and inviable microspores with defective exine and irregular unrestricted shape. RNA-seq analysis showed that the loss of function of GhGPAT12/25 affects the processes of wax metabolic, glycerol monomer biosynthesis, and transport. Consistently, cuticular waxes were dramatically reduced in mutant anthers. Yeast one-hybrid system (Y1H), virus-induced gene silencing (VIGS), and dual-luciferase (LUC) assays illustrated that GhMYB80s are likely to directly activate the expression of GhGPAT12/25. This study provides important insights for revealing the regulatory mechanism underlying anther development in cotton.

Friesodielsia subaequalis (Annonaceae): a new nomenclatural combination following conservation of the generic name against Schefferomitra

Friesodielsia (Annonaceae; Uvarieae) was erected by Van Steenis (1948: 458) to replace the illegitimate name Oxymitra (Blume 1830: 71) Hooker & Thomson (1855: 145), which was a later homonym of the liverwort Oxymitra Bischoff in Lindenberg (1829: 124). Although Van Steenis recognized 52 species in Friesodielsia from Africa and Asia, many taxonomists questioned whether the taxa in these two geographical regions were truly congeneric (e.g., Verdcourt 1971, Van Heusden 1992). The African and Asian species are morphologically distinct with regard to overall flower shape (broad vs elongate), inner petal arrangement (loosely coherent vs apically connivent), monocarp shape (moniliform vs subglobose), seed number per monocarp (up to five vs one or two) and pollen exine (coarsely verrucate vs echinate) (Verdcourt 1971, Walker 1971, Van Heusden 1992, Guo et al. 2017a).

Molecular regulation ofZmMs7required for maize male fertility and development of a dominant male-sterility system in multiple species

Understanding the molecular basis of male sterility and developing practical male-sterility systems are essential for heterosis utilization and commercial hybrid seed production in crops. Here, we report molecular regulation by genic male-sterility genemaize male sterility 7(ZmMs7) and its application for developing a dominant male-sterility system in multiple species.ZmMs7is specifically expressed in maize anthers, encodes a plant homeodomain (PHD) finger protein that functions as a transcriptional activator, and plays a key role in tapetal development and pollen exine formation. ZmMs7 can interact with maize nuclear factor Y (NF-Y) subunits to form ZmMs7-NF-YA6-YB2-YC9/12/15 protein complexes that activate target genes by directly binding to CCAAT box in their promoter regions. Premature expression ofZmMs7in maize by an anther-specific promoterp5126results in dominant and complete male sterility but normal vegetative growth and female fertility. Early expression ofZmMs7downstream genes induced by prematurely expressed ZmMs7 leads to abnormal tapetal development and pollen exine formation inp5126-ZmMs7maize lines. Thep5126-ZmMs7transgenic rice andArabidopsisplants display similar dominant male sterility. Meanwhile, themCherrygene coupled withp5126-ZmMs7facilitates the sorting of dominant sterility seeds based on fluorescent selection. In addition, both thems7-6007recessive male-sterility line andp5126-ZmMs7Mdominant male-sterility line are highly stable under different genetic germplasms and thus applicable for hybrid maize breeding. Together, our work provides insight into the mechanisms of anther and pollen development and a promising technology for hybrid seed production in crops.

Cytological and transcriptome analyses reveal OsPUB73 defect affects the gene expression associated with tapetum or pollen exine abnormality in rice

Background As one of the main crops in the world, sterility of rice (Oryza sativa L.) significantly affects the production and leads to yield decrease. Our previous research showed that OsPUB73, which encodes U-box domain-containing protein 73, may be associated with male sterility. However, little information is available on this gene that is required for anther development. In the present study, we knocked out OsPUB73 by using the CRISPR/Cas9 system and studied the cytological and transcriptome of the gene-defect associated with pollen development and sterility in the rice variety (Taichung 65). Results The sequence analysis indicated that OsPUB73 was comprised of 3 exons and 2 introns, of which CDS encoded 586 amino acids including a U-box domain. The expression pattern of OsPUB73 showed that it was highly expressed in the anther during meiosis stage. The ospub73 displayed low pollen fertility (19.45%), which was significantly lower than wild type (WT) (85.37%). Cytological observation showed tapetum vacuolated at the meiosis stage and pollen exine was abnormal at the bi-cellular pollen stage of ospub73. RNA-seq analysis detected 2240 down and 571 up-regulated genes in anther of ospub73 compared with WT during meiosis stage. Among of 2240 down-regulated genes, seven known genes were associated with tapetal cell death or pollen exine development, including CYP703A3 (Cytochrome P450 Hydroxylase703A3), CYP704B2 (Cytochrome P450 Hydroxylase704B2), DPW (Defective Pollen Wall), PTC1 (Persistant Tapetal Cell1), UDT1 (Undeveloped Tapetum1), OsAP37 (Aspartic protease37) and OsABCG15 (ATP binding cassette G15), which were validated by quantitative real-time polymerase chain reaction (qRT-PCR). These results suggested OsPUB73 may play an important role in tapetal or pollen exine development and resulted in pollen partial sterility. Conclusion Our results revealed that OsPUB73 plays an important role in rice male reproductive development, which provides valuable information about the molecular mechanisms of the U-box in rice male reproductive development.

Complementary Transcriptomic and Proteomic Analysis Reveals a Complex Network Regulating Pollen Abortion in GMS (msc-1) Pepper (Capsicum annuum L.)

Pepper (Capsicum annuum L.) is a globally important horticultural crop. Use of the genic male-sterile (GMS) line enables efficient commercial hybrid pepper seed production. However, the mechanisms of pepper GMS functioning remain unclear. In this study, we used proteomic and transcriptomic analysis to identify proteins and genes related to genic male sterility. A total of 764 differentially expressed proteins (DEPs) and 1069 differentially expressed genes (DEGs) were identified in the proteomic and transcriptomic level respectively, and 52 genes (hereafter “cor-DEGs-DEPs” genes) were detected at both levels. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified 13 DEPs and 14 DEGs involved in tapetum and pollen development. Among the 13 DEPs identified, eight were involved in pollen exine formation, and they were all up-regulated in the fertile line 16C1369B. For the 14 DEGs identified, ABORTED MICROSPORES (AMS) and DEFECTIVE IN TAPETAL DEVELOPMENT AND FUNCTION1 (TDF1) were involved in tapetum development, and both are possibly regulated by Msc-1. All of these genes were detected and confirmed by qRT-PCR. The presence of these genes suggests their possible role in tapetum and pollen exine formation in GMS pepper. Most key genes and transcription factors involved in these processes were down-regulated in the sterile line 16C1369A. This study provides a better understanding of GMS (msc-1) molecular functioning in pepper.

The atypically high modulus of pollen exine

Sporopollenin, the polymer comprising the exine (outer solid shell) of pollen, is recognized as one of the most chemically and mechanically stable naturally occurring organic substances. The elastic modulus of sporopollenin is of great importance to understanding the adhesion, transport and protective functions of pollen grains. In addition, this fundamental mechanical property is of significant interest in using pollen exine as a material for drug delivery, reinforcing fillers, sensors and adhesives. Yet, the literature reports of the elastic modulus of sporopollenin are very limited. We provide the first report of the elastic modulus of sporopollenin from direct indentation of pollen particles of three plant species: ragweed ( Ambrosia artemisiifolia ), pecan ( Carya illinoinensis ) and Kentucky bluegrass ( Poa pratensis ). The modulus was determined with atomic force microscopy by using direct nanomechanical mapping of the pollen shell surface. The moduli were atypically high for non-crystalline organic biomaterials, with average values of 16 ± 2.5 GPa (ragweed), 9.5 ± 2.3 GPa (pecan) and 16 ± 4.0 GPa (Kentucky bluegrass). The amorphous pollen exine has a modulus exceeding known non-crystalline biomaterials, such as lignin (6.7 GPa) and actin (1.8 GPa). In addition to native pollen, we have investigated the effects of exposure to a common preparative base–acid chemical treatment and elevated humidity on the modulus. Base–acid treatment reduced the ragweed modulus by up to 58% and water vapour exposure at 90% relative humidity reduced the modulus by 54% (pecan) and 72% (Kentucky bluegrass). These results are in agreement with recently published estimates of the modulus of base–acid-treated ragweed pollen of 8 GPa from fitting to mechanical properties of ragweed pollen–epoxy composites.