Altered callose deposition during embryo sac formation of multi-pistil mutant (mp1) in Medicago sativa

Abstract

ABSTRACT. Whether callose deposition is the cause or result of ovule sterility in Medicago sativa remains controversial, because it is unclear when and where changes in callose deposition and dissolution occur during fertile and sterile embryo sac formation. Here, alfalfa spontaneous multi-pistil mutant (mp1) and wild-type plants were used to compare the dynamics of callose deposition during embryo sac formation using microscopy. The results showed that both mutant and wild-type plants experienced megasporogenesis and megagametogenesis, and there was no significant difference during megasporogenesis. In contrast to the wild-type plants, in which the mature embryo sac was observed after three continuous cycles of mitosis, functional megaspores of mutant plants developed abnormally after the second round of mitosis, leading to degeneration of synergid, central, and antipodal cells. Callose deposition in both mutant and wild-type plants was first observed in the walls of megasporocytes, and then in the megaspore tetrad walls. After meiosis, the callose wall began to degrade as the functional megaspore underwent mitosis, and almost no callose was observed in the mature embryo sac in wild-type plants. However, callose deposition was observed in mp1 plants around the synergid, and increased with the development of the embryo sac, and was mainly deposited at the micropylar end. Our results indicate that synergid, central, and antipodal cells, which are surrounded by callose, may degrade owing to lack of nutrition. Callose accumulation around the synergid and at the micropylar end may hinder signals required for the pollen tube to enter the embryo sac, leading to abortion.

Type II arabinogalactans initiated by hydroxyproline‐O‐galactosyltransferases play important roles in pollen–pistil interactions

“…Callose is a cell wall β‐1,3‐glucan polymer that plays an essential role in plant reproductive processes such as megasporogenesis (Newbigin et al, 2009; Zhou, 2019). It is also involved in pollen–pistil interactions in plants, acting as a marker for abnormal ovule development and affecting micropylar PT guidance (Zhou et al, 2016). The callose accumulation observed in the reciprocal crosses between galt25789 pistils and WT PGs (22%) indicates a defect of female origin.…”

Female gametophyte expressedArabidopsis thalianalipid transfer proteins AtLtpI.4 and AtLtpI.8 provide a link between callose homeostasis, pollen tube guidance, and fertilization success

“…While pollen tube germination and growth along the transmitting tract was wild-type-like in the mutant, our results showed that the concomitant loss of both, AtLTP1.4 and AtLTP1.8 gene functions, caused aberrant callose deposition patterns in the ltp1.4/1.8 mutant ovules. Callose represents a cell wall β-1,3-glucan polymer and alike for other angiosperms, in wild-type Arabidopsis plants plays an essential role during megasporogenesis (Newbigin et al, 2009; Zhou et al, 2016) of female reproductive development. Typically, callose deposition is first observed in the wall of the megasporocyte, and after meiosis in the walls of the megaspore tetrad (Schneitz et al, 1995).…”

The SAP function in pistil development was proved by two allelic mutations in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

“…Among the floral organs, the pistil has the most complex structure, and its reproductive growth and development processes are regulated by a large number of transcription factors and functional genes [5][6][7]. Several genes regulating pistil development and physiological and biochemical changes during pistil abortion have been identified through mapping and cloning of female sterile mutant genes in Arabidopsis thaliana, rice, cotton, maize, and rapeseed, leading to a gradual understanding of the morphological model and genetic regulation of pistil development [8][9][10][11][12].…”