SlTDP1 Is Required To Specify Tapetum Identity And For The Regulation Of Redox Homeostasis In Tomato Anthers

ABSTRACTThe tapetum is a specialized layer of cells within the anther adjacent to the sporogenic tissue. During its short life, it provides nutrients, molecules and materials to the pollen mother cells and microsporocytes being essential during callose degradation and pollen wall formation. However, the acquisition of tapetal cell identity in tomato plants is a process still poorly understood. We report here the identification and characterization of SlTPD1 (Solanum lycopersicum TPD1), a gene specifically required for pollen development in tomato plants. Gene editing was used to generate loss-of-function Sltpd1 mutants that showed absence of tapetal tissue. In these plants, sporogenous cells developed but failed to complete meiosis resulting in complete male sterility. Transcriptomic analysis conducted in wild-type and mutant anthers at an early stage revealed the down regulation of a set of genes related to redox homeostasis. Indeed, Sltpd1 anthers showed a reduction of reactive oxygen species (ROS) accumulation at early stages and altered activity of ROS scavenging enzymes. The obtained results highlight the importance of ROS homeostasis in the interaction between the tapetum and the sporogenous tissue in tomato plants.One sentence summaryThe small protein SlTPD1 is required for tapetum formation in tomato, highlighting the role of this tissue in the regulation of redox homeostasis during male gametogenesis.

Genesis of the generative structures Platycodon grandiflorus (family Сampanulaceae)

The article presents the research results of the genesis of the elements of the microsporangium wall, sporogenous tissue, microspores, megaspores, male and female gametophytes of the Platycodon grandiflorus . The types of formation of the structures mail generative sphere (dicotyledonous type of microsporangium wall formation, simultaneous type of the tetrad microspores development, 3-cells of the pollen grains with 6-th pores, Polygonum - type of the formation embryo sac) have been established. A high viability of pollen grains was established during pollination and possibility of obtaining complete seeds when growing this species in the conditions of the Southern Coast of the Crimea.

Comparative analysis of anther development in natural populations indicate premature degradation of sporogenous tissue as a cause of male sterility in Gaultheria fragrantissima

Gaultheria fragrantissima Wall. (Ericaceae) is a gynodioecious species having both hermaphrodite and male sterile plants. In this study, we present a comparative analysis of the different stages of anther development in naturally occuring hermaphrodite and male sterile populations of G. fragrantissima found in Meghalaya, India. While hermaphrodite flowers had well developed anther lobes, the male sterile flowers formed a white unorganized mass of tissues with a tuft of hairy outgrowth at the tip of the stamens. Histological analyses of progressive anther development in both the lines indicate an abnormal development of the sporogenous tissue in the developing anthers in the male steril line. While anther development in the hermaphrodite line was of the dicotyledonous type, the anthers of male sterile line showed progressive degradation of the sporogenous tissues and wall layers. Pollen development was also disrupted in male sterile line resulting in distorted pollen due to the irregular projection of exine wall. Our results suggest that premature degradation of the sporogenous tissues during anther development determines male sterility in G. fragrantissima.

Seasonal temperature variations influence tapetum mitosis patterns associated with reproductive fitness

Environmental stress in plants impacts many biological processes, including male gametogenesis, and affects several cytological mechanisms that are strongly interrelated. To understand the likely impact of rising temperature on reproductive fitness in the climate change regime, a study of tapetal mitosis and its accompanying meiosis over seasons was made to elucidate the influence of temperature change on the cytological events occurring during microsporogenesis. For this we used two species of an environmentally sensitive plant system, i.e., genus Cymbopogon Sprengel (Poaceae), namely Cymbopogon nardus (L.) Rendle var. confertiflorus (Steud.) Bor (2n = 20) and Cymbopogon jwaruncusha (Jones) Schult. (2n = 20). Both species flower profusely during extreme summer (48 °C) and mild winter (15 °C) but support low and high seed fertility, respectively, in the two seasons. We have shown that tapetal mitotic patterns over seasons entail differential behavior for tapetal mitosis. During the process of tapetum development there are episodes of endomitosis that form either (i) an endopolyploid genomically imbalanced uninucleate and multinucleate tapetum, and (or) (ii) an acytokinetic multinucleate genomically balanced tapetum, with the progression of meiosis in the accompanying sporogenous tissue. The relative frequency of occurrence of the two types of tapetum mitosis patterns is significantly different in the two seasons, and it is found to be correlated with the temperature conditions. Whereas, the former (genomically imbalanced tapetum) are prevalent during the hot summer, the latter (genomically balanced tapetum) are frequent under optimal conditions. Such a differential behaviour in tapetal mitosis vis-à-vis temperature change is also correspondingly accompanied by substantial disturbances or regularity in meiotic anaphase disjunction. Both species show similar patterns. The study underpins that tapetal mitotic behaviour per se could be a reasonable indicator to elucidate the effect of climate change on reproductive fitness.

Microsporogenesis and pollen grains in Silene dioica (L.) Cl. and alterations in its anthers parasited by Ustilago violacea (Pers.) Rouss. (Ustilaginales)

Healthy and infected anthers are comparatively studied with optical and electron microscopic techniques. The fungus stops the stamen histogenesis at an early stage and destroys specifically the sporogenous tissue.

Ultrastructural studies on the sporogenous tissue and anther wall of Leucojum aestivum (amaryllidaceae) in different developmental stages

In this study, ultrastructures of anther wall and sporogenous tissue of Leucojum aestivum were investigated during different developmental stages. Cytomictic channels were seen between pollen mother cells during prophase I. Polar distribution was described in the organelle content of pollen mother cells and microspores in early phases of microsporogenesis and also in pollen mitosis. Active secretion was observed in tapetal cells. Previous reports about developmental stages of male gametophyte were compared with the results of this study.

CYTOHISTOLOGY OF A 2–2–4 TYPE SPORT IN BARTLETT PEAR (Pyrus Communis)

In the 1980' s, a Bartlett pear giant fruit sport was found in Pingdu, Shandong. The characteristics of mutation are larger fruit, thicker branch, shorter internode and much more spur. By grafting propagation, the clones began to bear fruit in 1990, and maintain the characteristics of variable mother plant. From microspore formation to blossom and spreading pollen, the cytohistological observation of sport flowering organs indicates: in every phase of pollen development, the size of florets, anthers and pollen grains are similar to CK; their pollen types both belong to tricolporat, pollen grains are nearly equal in size. This indicates that sport sporogenous tissue do not mutate. The observation of shoot apex sections showes: for CK, the cells of three histogenic layers range regularly; the size of cells, nuclei, and nucleoli among LI, LII, LIII are similar. For sport, the cells of LI, LII are no difference from CK, but in LIII and inner tissue, cells, nuclei, nucleoli all become larger clearly. This indicates LIII had mutated. So this sport is a 2–2–4 type chimera.

Microsporogenesis in the normal and male-sterile stamenIess-2 mutant of tomato (Lycopersicon esculentum)

The development of microspores and the associated changes in the tapetum were examined in the normal (+/+) and male-sterile, stamenless-2 (sl-2/sl-2) mutant anthers of tomato (Lycopersicon esculentum). Anthers of eight comparable stages, from the microspore mother cell stage to anthesis, of both lines were processed for light microscopy. Until the formation of tetrads (stage ii), there were no differences in the sporogenous tissue, but the tapetal cells of the mutant were more enlarged than the normal and had, at places, divided to form a bilayer. Later, the tapetal cells in both lines became amoeboid and had sporopollenin-like deposits. At stage iv, whereas the tapetal cells of the normal had started to degenerate, those of the mutant were intact but had large vacuoles. Also at this stage, the deposition of exine was evident in normal microspores, but it was lacking in most mutant microspores, which enlarged considerably and eventually degenerated. From stage v onwards, the normal microspores progressed from the binucleate pollen to pollen containing many vacuoles to mature pollen. In the mutant, tapetum degeneration was delayed until stage v, and later, although some microspores closer to the tapetum appeared normal, most either were empty or had large vacuoles. It is suggested that the delay in tapetum degeneration coupled with the failure of exine deposition, presumably associated with low esterase activity, is responsible for pollen degeneration in the sl-2/sl-2 mutant.