Observation of female gamete (Carpogonia) germination of Porphyra yezoensis and P. oligospermatangia

Several papers have reported that part or whole leafy thallus seemingly consisting of zygotospores can give rise to both blades and conchocelis in the same culture of Porphyra. Study on samples of wild and cul- tivated Porphyra yezoensis and P. oligospermatangia were conducted to clarify the origination of the young blades in the culture. It is confirmed that single cells on the blade of both species, which normally intermixed with zygotospores, germinated into young blades. TEM and SEM observation has shown that the single cells of Porphyra yezoensis had typical features of female gamete (carpogonia) but archeospore. Therefore, the female gametes are responsible in developing leafy thalli.

A reciprocal inhibition between ARID1 and MET1 in male and female gametes in Arabidopsis

Both female and male gametophytes harbor companion cells and gametes. MET1, a DNA methyltransferase, is down-regulated in companion cells. However, how MET1 is differentially regulated in gametophytes remains unexplored. ARID1, a transcription factor that is specifically depleted in sperm cells, is occupied by MET1- dependent CG methylation. Here, we show that MET1 confines ARID1 to the vegetative cell of male gametes, but ARID1 conversely represses MET1 in the central cell of female gametes. Compared to the vegetative celllocalization in wild type pollen, ARID1 expands to sperm cells in the met1 mutant. To understand whether MET1- dependent ARID1 inhibition exists during female gametogenesis, we first show that ARID1 is expressed in the megaspore mother cell （MMC）, ARID1 but not MET1 is detectable in the central cell at maturity. Interestingly, compared to the absence of MET1 in the central cell and the egg cell of wild type ovules, MET1 significantly accumulates in these two cells in aridl ovules. Lastly, we show that both ARIDI and METI are required for the cell specification of MMC. Collectively, our results uncover a reciprocal dependence between ARIDI and METI, and provide a clue to further understand how the specification of MMC is likely regulated by DNA methylation.

Production of aneuhaploid and euhaploid sporocytes by meiotic restitution in fertile hybrids between durum wheat Langdon chromosome substitution lines and Aegilops tauschii

Fertile F1 hybrids were obtained between durum wheat （Triticum durum Desf.） Langdon （LDN） and its 10 disomic substitution （LDN DS） lines with Aegilops tauschii accession AS60 without embryo rescue. Selfed seedset rates for hybrids of LDN with AS60 were 36.87% and 49.45% in 2005 and 2006, respectively. Similar or higher selfed seedset rates were observed in the hybrids of 1D （1A）, 1D （1B）, 3D （3A）, 4D （4B）, 7D （7A）, and 2D （2B） with AS60, while lower in hybrids of 3D （3B） ＋ 3BL, 5D （5A） ＋ 5AL, 5D （5B） ＋ 5B and 6D （6B） ＋ 6BS with AS60 compared with the hybrids of LDN with AS60. Observation of male gametogenesis showed that meiotic restitution, both first-division restitution （FDR） and single-division meiosis （SDM） resulted in the formation of functional unreduced gametes, which in turn produced seeds. Both euhaploid and aneuhaploid gametes were produced in F1 hybrids. This suggested a strategy to simultaneously transfer and locate major genes from the ancestral species T. turgidum or Ae. tauschii. Moreover, there was no significant difference in the aneuhaploid rates between the F1 hybrids of LDN and LDN DS lines with AS60, suggesting that meiotic pairing between the two D chromosomes in the hybrids of LDN DS lines with AS60 did not promote the formation of aneuhaploid gametes.