Mitochondrial DNA genetic polymorphism in thirteen rice cytoplasmic male sterile lines

Key message

Thirteen rice CMS lines derived from different cytoplasms were classified into eight groups by PCR amplification on mtDNA. The orf79 gene, which causes Boro II CMS, possibly results in Dian1-CMS.

Abstract

Thirteen rice cytoplasmic male sterile (CMS) lines derived from different cytoplasms are widely used for hybrid rice breeding. Based on 27 loci on mitochondrial DNA, including single nucleotide polymorphisms and segmental sequence variations between typical indica and japonica as well as high-polymorphism segmental sequence variations and single nucleotide polymorphisms among rice CMS lines, the 13 rice CMS lines were classified into eight groups: (I) wild-abortive CMS, Indonesian Shuitiangu CMS, K-CMS, Gang CMS, D-CMS and dwarf abortive CMS; (II) Maxie-CMS; (III) Honglian CMS; (IV) Boro II CMS; (V) Dian1-CMS; (VI) Liao-CMS; (VII) Lead CMS; and (VIII) Chinese wild rice CMS. According to their pollen abortion phenotypes, groups I and II (including 7 CMS lines) were classified as sporophytic CMS lines, the cytoplasmic genetic relationships among which were very close. They could have originated from similar, or even the same, cytoplasm donors. Groups III–VIII (including 6 CMS lines) were categorized as gametophytic CMS lines, the cytoplasms of which differed from one another, with some having relatively far genetic relationships. Dian1-CMS was found to harbor the orf79 gene, which causes Boro II CMS, whereas Liao-CMS had an orf79 structure that does not result in Lead CMS. Therefore, we speculated that orf79 is associated with Dian1-CMS but not with Liao-CMS. The atp6–orf79 structure related to sterility was also found to experience multiple evolutionary turnovers. All sporophytic CMS lines were indica-like. Except the Honglian CMS line, which was indica-like, all gametophytic CMS lines were japonica-like.     

Contrasting hypoxia tolerance and adaptation in Malus species is linked to differences in stomatal behavior and photosynthesis

We examined the potential differences in tolerance to hypoxia by two species of apple rootstocks. Stomatal behavior and photosynthesis were compared between Malus sieversii and Malus hupehensis. Plants were hydroponically grown for 15 days in normoxic or hypoxic nutrient solutions. Those of M. sieversii showed much greater sensitivity, with exposure to hypoxia resulting in higher leaf concentrations of abscisic acid (ABA) that prompted stomatal closure. Compared with the control plants of that species, stomatal density was greater in both new and mature leaves under stress conditions. In contrast, stomatal density was significantly decreased in leaves from M. hupehensis, while stomatal length was unaffected. Under stress, the net photosynthetic rate, stomatal conductance and chlorophyll contents were markedly reduced in M. sieversii. The relatively hypoxia‐tolerant genotype M. hupehensis, however, showed only minor changes in net photosynthesis or chlorophyll content, and only a slight decrease in stomatal conductance due to such treatment. Therefore, we conclude that the more tolerant M. hupehensis utilizes a better protective mechanism for retaining higher photosynthetic capacity than does the hypoxia‐sensitive M. sieversii. Moreover, this contrast in tolerance and adaptation to stress is linked to differences in their stomatal behavior, photosynthetic capacity and possibly their patterns of native distribution.     

MAIGO2 is involved in abscisic acid‐mediated response to abiotic stresses and Golgi‐to‐ER retrograde transport

The central role of multisubunit tethering complexes in intracellular trafficking has been established in yeast and mammalian systems. However, little is known about their roles in the stress responses and the early secretory pathway in Arabidopsis. In this study, Maigo2 (MAG2), which is equivalent to the yeast Tip20p and mammalian Rad50‐interacting protein, is found to be required for the responses to salt stress, osmotic stress and abscisic acid in seed germination and vegetative growth, and MAG2‐like (MAG2L) is partially redundant with MAG2 in response to environmental stresses. MAG2 strongly interacts with the central region of ZW10, and both proteins are important as plant endoplasmic reticulum (ER)‐stress regulators. ER morphology and vacuolar protein trafficking are unaffected in the mag2, mag2l and zw10 mutants, and the secretory marker to the apoplast is correctly transported in mag2 plants, which indicate that MAG2 functions as a complex with ZW10, and is potentially involved in Golgi‐to‐ER retrograde trafficking. Therefore, a new role for ER–Golgi membrane trafficking in abiotic‐stress and ER‐stress responses is discovered.     

Mechanistic studies of perfluorooctane sulfonate, perfluorooctanoic acid uptake by maize (Zea mays L. cv. TY2)

Aims

There is a need to predict trace metal concentration in plant organs at given development stages. The aim of this work was to describe the Cd hyperaccumulation kinetics in the different plant organs, throughout the complete cultivation cycle, independently of a possible soil effect.

Methods

Plants of Noccaea caerulescens were exposed in aeroponics to three constantly low Cd concentrations and harvested at 6 to 11 dates, until siliquae formation.

Results

Dry matter allocation between roots and shoots was constant over time and exposure concentrations, as well as Cd allocation. However 86 % of the Cd taken up was allocated to the shoots. Senescent rosette leaves showed similar Cd concentrations to the living ones, suggesting no redistribution from old to young organs. The Cd root influx was proportional to the exposure concentration and constant over time, indicating that plant development had no effect on this. The bio-concentration factor (BCF), i.e. [Cd]_plant/[Cd²⁺]_solution for the whole plant, roots or shoots was independent of the exposure concentration and of the plant stage.

Conclusions

Cadmium uptake in a given plant part could therefore be predicted at any plant stage by multiplying the plant part dry matter by the corresponding BCF and the Cd²⁺ concentration in the exposure solution.     

Magnesium transporters and their role in Al tolerance in plants

Magnesium (Mg) is an essential macronutrient for plant growth, which has diverse biological functions. However, little is known about the transport system of this nutrient in plants. In the genome of plants such as rice and Arabidopsis, there are homologues of bacterial Mg transporters (CorA) and some of them have been functionally characterized, but the physiological role of these transporters are poorly understood. On the other hand, Mg is able to alleviate Al toxicity in a number of plant species, but the mechanisms underlying this alleviation are not well understood. Recently, this alleviation has been associated with a Mg transporter in rice. In this paper, we present our opinions on Mg transporters, which are required for uptake, translocation, distribution and storage in plants. Possible mechanisms for Mg-mediated alleviation of Al toxicity are also discussed.     

Effect of aboveground intervention on fine root mass, production, and turnover rate in a Chinese cork oak (Quercus variabilis Blume) forest

Aims

Fine root is an important part of the forest carbon cycle. The growth of fine roots is usually affected by forest intervention. This study aims to investigate the fine root mass, production, and turnover in the disturbed forest.

Methods

The seasonal and vertical distributions of fine root (diameter ≤2 mm) were measured in a Chinese cork oak (Quercus variabilis Blume) forest. The biomass and necromass of roots with diameters ≤1 mm and 1-2 mm in 0-40 cm soil profiles were sampled by using a sequential soil coring method in the stands after clear cutting for 3 years, with the stands of the remaining intact trees as the control.

Results

The fine root biomass (FRB) and fine root necromass (FRN) varied during the growing season and reached their peak in August. Lower FRB and higher FRN were found in the clear cutting stands. The ratio between FRN and FRB increased after forest clear cutting compared with the control and was the highest in June. The root mass with diameter ≤1 mm was affected proportionately more than that of diameter 1-2 mm root. Clear cutting reduced FRB and increased FRN of roots both ≤1 mm and 1-2 mm in diameter along the soil depths. Compared with the control, the annual fine root production and the average turnover rate decreased by 30.7 % and 20.7 %, respectively, after clear cutting for 3 years. The decline of canopy cover contributed to the dramatic fluctuation of soil temperature and moisture from April to October. With redundancy discriminate analysis (RDA) analysis, the first axis was explained by soil temperature (positive) and moisture (negative) in the control stands. Aboveground stand structure, including canopy cover, sprout height, and basal area, influenced FRB and FRN primarily after forest clear cutting.

Conclusions

This study suggested that the reduction of fine root biomass, production, and turnover rate can be attributed to the complex changes that occur after forest intervention, including canopy damage, increased soil temperature, and degressive soil moisture.     

Organisation of the endosperm and endosperm–placenta syncytia in bladderworts (Utricularia, Lentibulariaceae) with emphasis on the microtubule arrangement

Multinucleate cells play an important role in higher plants, especially during reproduction; however, the configurations of their cytoskeletons, which are formed as a result of mitosis without cytokinesis, have mainly been studied in coenocytes. Previous authors have proposed that in spite of their developmental origin (cell fusion or mitosis without cytokinesis), in multinucleate plant cells, radiating microtubules determine the regular spacing of individual nuclei. However, with the exception of specific syncytia induced by parasitic nematodes, there is no information about the microtubular cytoskeleton in plant heterokaryotic syncytia, i.e. when the nuclei of fused cells come from different cell pools. In this paper, we describe the arrangement of microtubules in the endosperm and special endosperm–placenta syncytia in two Utricularia species. These syncytia arise from different progenitor cells, i.e. cells of the maternal sporophytic nutritive tissue and the micropylar endosperm haustorium (both maternal and paternal genetic material). The development of the endosperm in the two species studied was very similar. We describe microtubule configurations in the three functional endosperm domains: the micropylar syncytium, the endosperm proper and the chalazal haustorium. In contrast to plant syncytia that are induced by parasitic nematodes, the syncytia of Utricularia had an extensive microtubular network. Within each syncytium, two giant nuclei, coming from endosperm cells, were surrounded by a three-dimensional cage of microtubules, which formed a huge cytoplasmic domain. At the periphery of the syncytium, where new protoplasts of the nutritive cells join the syncytium, the microtubules formed a network which surrounded small nuclei from nutritive tissue cells and were also distributed through the cytoplasm. Thus, in the Utricularia syncytium, there were different sized cytoplasmic domains, whose architecture depended on the source and size of the nuclei. The endosperm proper was isolated from maternal (ovule) tissues by a cuticle layer, so the syncytium and chalazal haustorium were the only way for nutrients to be transported from the maternal tissue towards the developing embryo.