Comparisons of early transcriptome responses to low-oxygen environments in three dicotyledonous plant species.

Waterlogging is a serious impediment to crop productivity worldwide which acts to reduce oxygen levels in the rhizosphere due to the low diffusion rate of molecular oxygen in water. Plants respond to low oxygen through rapid and specific changes at both the transcriptional and translational levels. Transcriptional changes to low-oxygen (hypoxia) stress have been studied in a number of plant species using whole genome microarrays. Using transcriptome data from root tissue from early time points (4-5 h) from cotton (Gossypium hirsutum), Arabidopsis and gray poplar (Populus x canescens), we have identified a core set of orthologous genes that responded to hypoxia in similar ways between species, and others that showed species specific responses . Responses to hypoxia were most similar between Arabidopsis and cotton, while the waterlogging tolerant poplar species exhibited some significant differences.

Global gene expression responses to waterlogging in roots and leaves of cotton (Gossypium hirsutum L.).

Waterlogging stress causes yield reduction in cotton (Gossypium hirsutum L.). A major component of waterlogging stress is the lack of oxygen available to submerged tissues. While changes in expressed protein, gene transcription and metabolite levels have been studied in response to low oxygen stress, little research has been done on molecular responses to waterlogging in cotton. We assessed cotton growth responses to waterlogging and assayed global gene transcription responses in root and leaf cotton tissues of partially submerged plants. Waterlogging caused significant reductions in stem elongation, shoot mass, root mass and leaf number, and altered the expression of 1,012 genes (4% of genes assayed) in root tissue as early as 4 h after flooding. Many of these genes were associated with cell wall modification and growth pathways, glycolysis, fermentation, mitochondrial electron transport and nitrogen metabolism. Waterlogging of plant roots also altered global gene expression in leaf tissues, significantly changing the expression of 1,305 genes (5% of genes assayed) after 24 h of flooding. Genes affected were associated with cell wall growth and modification, tetrapyrrole synthesis, hormone response, starch metabolism and nitrogen metabolism The implications of these results for the development of waterlogging-tolerant cotton are discussed.

Pollen-mediated gene flow from transgenic safflower (Carthamus tinctorius L.) intended for plant molecular farming to conventional safflower.

Field experiments were conducted in Chile and western Canada to measure short-distance (0 to 100 m) outcrossing from transgenic safflower (Carthamus tinctorius L.) intended for plant molecular farming to non-transgenic commodity safflower of the same variety. The transgenic safflower used as the pollen source was transformed with a construct for seed-specific expression of a high-value protein and constitutive expression of a gene conferring resistance to the broad-spectrum herbicide glufosinate. Progeny of non-transgenic plants grown in plots adjacent to the transgenic pollen source were screened for glufosinate resistance to measure outcrossing frequency. Outcrossing frequency differed among locations: values closest to the transgenic pollen source (0 to 3 m) ranged from 0.48 to 1.67% and rapidly declined to between 0.0024 to 0.03% at distances of 50 to 100 m. At each location, outcrossing frequency was spatially heterogeneous, indicating insects or wind moved pollen asymmetrically. A power analysis assuming a binomial distribution and a range of alpha values (type 1 error) was conducted to estimate an upper and lower confidence interval for the probable transgenic seed frequency in each sample. This facilitated interpretation when large numbers of seeds were screened from the outcrossing experiments and no transgenic seeds were found. This study should aid regulators and the plant molecular farming industry in developing confinement strategies to mitigate pollen mediated gene flow from transgenic to non-transgenic safflower.

The low-oxygen-induced NAC domain transcription factor ANAC102 affects viability of Arabidopsis seeds following low-oxygen treatment.

Low-oxygen stress imposed by field waterlogging is a serious impediment to plant germination and growth. Plants respond to waterlogging with a complex set of physiological responses regulated at the transcriptional, cellular, and tissue levels. The Arabidopsis (Arabidopsis thaliana) NAC domain-containing gene ANAC102 was shown to be induced under 0.1% oxygen within 30 min in both roots and shoots as well as in 0.1% oxygen-treated germinating seeds. Overexpression of ANAC102 altered the expression of a number of genes, including many previously identified as being low-oxygen responsive. Decreasing ANAC102 expression had no effect on global gene transcription in plants but did alter expression patterns in low-oxygen-stressed seeds. Increasing or decreasing the expression of ANAC102 did not affect adult plant survival of low-oxygen stress. Decreased ANAC102 expression significantly decreased germination efficiency following a 0.1% oxygen treatment, but increased expression had no effect on germination. This protective role during germination appeared to be specific to low-oxygen stress, implicating ANAC102 as an important regulator of seed germination under flooding.