Desiccation tolerance of Botryococcus braunii (Trebouxiophyceae, Chlorophyta) and extreme temperature tolerance of dehydrated cells

Botryococcus braunii Kützing, a green colonial microalga, occurs worldwide in both freshwater and brackish water environments. Despite considerable attention to B. braunii as a potential source of renewable fuel, many ecophysiological properties of this alga remain unknown. Here, we examined the desiccation and temperature tolerances of B. braunii using two newly isolated strains BOD-NG17 and BOD-GJ2. Both strains survived through 6- and 8-month desiccation treatments but not through a 12-month treatment. Interestingly, the desiccation-treated cells of B. braunii gained tolerance to extreme temperature shifts, i.e., high temperature (40 °C) and freezing (−20 °C). Both strains survived for at least 4 and 10 days at 40 and −20 °C, respectively, while the untreated cells barely survived at these temperatures. These traits would enable long-distance dispersal of B. braunii cells and may account for the worldwide distribution of this algal species. Extracellular substances such as polysaccharides and hydrocarbons seem to confer the desiccation tolerance

Kinesin-4 Functions in Vesicular Transport on Cortical Microtubules and Regulates Cell Wall Mechanics during Cell Elongation in Plants.

This is the accepted manuscript. The final version is available at http://www.cell.com/molecular-plant/abstract/S1674-2052%2815%2900091-X.In plants, anisotropic cell expansion depends on cortical microtubules that serve as tracks along which macromolecules and vesicles are transported by the motor kinesins of unknown identities. We used cotton (Gossypium hirsutum) fibers that underwent robust elongation to discover kinesins that are involved in cell elongation and found Gh KINESIN-4A expressed abundantly. The motor was detected by immunofluorescence on vesicle-like structures that were associated with cortical microtubules. In Arabidopsis thaliana, the orthologous motor At KINESIN-4A/FRA1, previously implicated in cellulose deposition during secondary growth in fiber cells, was examined by live-cell imaging in cells expressing the fluorescently tagged functional protein. The motor decorated vesicle-like particles that exhibit a linear movement along cortical microtubules with an average velocity of 0.89 μm/min, which was significantly different from those linked to cellulose biosynthesis. We also discovered that At KINESIN-4A/FRA1 and the related At KINESIN-4C play redundant roles in cell wall mechanics, cell elongation, and the axial growth of various vegetative and reproductive organs, as the loss of At KINESIN-4C greatly enhanced the defects caused by a null mutation at the KINESIN-4A/FRA1 locus. The double mutant displayed a lack of cell wall softening at normal stages of rapid cell elongation. Furthermore, enhanced deposition of arabinose-containing carbohydrate was detected in the kinesin-4 mutants. Our findings established a connection between the Kinesin-4-based transport of cargoes containing non-cellulosic components along cortical microtubules and cell wall mechanics and cell elongation in flowering plants.This report is based on work supported by the National Science Foundation under grant MCB-1243959 (BL and YRJL), Physical Biosciences Program of the Office of Basic Energy Sciences of the U.S. Department of Energy under the contracts DE-FG02-04ER15554 (BL) and DEFG02- 03ER15415 (Z-HY). SL is supported by the Center for LignoCellulose Structure and Formation, an Energy Frontier Research Center funded by the U.S. Department of Energy under the award DE-SC0001090 and SAB is supported by a Gatsby Foundation Fellowship

An unidentified ultraviolet-B-specific photoreceptor mediates transcriptional activation of the cyclobutane pyrimidine dimer photolyase gene in plants

Cyclobutane pyrimidine dimers (CPDs) constitute a majority of DNA lesions caused by ultraviolet-B (UVB). CPD photolyase, which rapidly repairs CPDs, is essential for plant survival under sunlight containing UVB. Our earlier results that the transcription of the cucumber CPD photolyase gene (CsPHR) was activated by light have prompted us to propose that this light-driven transcriptional activation would allow plants to meet the need of the photolyase activity upon challenges of UVB from sunlight. However, molecular mechanisms underlying the light-dependent transcriptional activation of CsPHR were unknown. In order to understand spectroscopic aspects of the plant response, we investigated the wavelength-dependence (action spectra) of the light-dependent transcriptional activation of CsPHR. In both cucumber seedlings and transgenic Arabidopsis seedlings expressing reporter genes under the control of the CsPHR promoter, the action spectra exhibited the most predominant peak in the long-wavelength UVB waveband (around 310 nm). In addition, a 95-bp cis-acting region in the CsPHR promoter was identified to be essential for the UVB-driven transcriptional activation of CsPHR. Thus, we concluded that the photoperception of long-wavelength UVB by UVB photoreceptor(s) led to the induction of the CsPHR transcription via a conserved cis-acting element

Ozone-Induced Rice Grain Yield Loss Is Triggered via a Change in Panicle Morphology That Is Controlled by ABERRANT PANICLE ORGANIZATION 1 Gene.

Rice grain yield is predicted to decrease in the future because of an increase in tropospheric ozone concentration. However, the underlying mechanisms are unclear. Here, we investigated the responses to ozone of two rice (Oryza Sativa L.) cultivars, Sasanishiki and Habataki. Sasanishiki showed ozone-induced leaf injury, but no grain yield loss. By contrast, Habataki showed grain yield loss with minimal leaf injury. A QTL associated with grain yield loss caused by ozone was identified in Sasanishiki/Habataki chromosome segment substitution lines and included the ABERRANT PANICLE ORGANIZATION 1 (APO1) gene. The Habataki allele of the APO1 locus in a near-isogenic line also resulted in grain yield loss upon ozone exposure, suggesting APO1 involvement in ozone-induced yield loss. Only a few differences in the APO1 amino acid sequences were detected between the cultivars, but the APO1 transcript level was oppositely regulated by ozone exposure: i.e., it increased in Sasanishiki and decreased in Habataki. Interestingly, the levels of some phytohormones (jasmonic acid, jasmonoyl-L-isoleucine, and abscisic acid) known to be involved in attenuation of ozone-induced leaf injury tended to decrease in Sasanishiki but to increase in Habataki upon ozone exposure. These data indicate that ozone-induced grain yield loss in Habataki is caused by a reduction in the APO1 transcript level through an increase in the levels of phytohormones that reduce leaf damage

Genome scans for ozone-induced yield loss and the number of primary rachis branches.

<p>(A, C) QTL likelihood maps for (A) grain yield and (C) the number of primary rachis branches. Genetic maps were produced by composite interval mapping using differences between ambient air and elevated ozone. (B, D) Additive effect of (B) QTLs for grain yield and (D) the number of primary rachis branches. A positive (negative) additive effect in <i>B</i> and <i>D</i> represents an increasing allele from Sasanishiki (Habataki). The vertical dotted lines separate chromosomes 1–12 (labeled at the bottom) progressing left to right along the <i>x</i>-axis.</p

Effects of elevated ozone on two rice cultivars, Sasanishiki and Habataki.

<p>(A) Changes in grain yield in 2009 and 2010. (B) Changes in the number of primary rachis branches in 2009 and 2010. Values are mean ± SD (<i>n</i> = 20). Error bars indicate SD; n.s., not significant; *<i>P</i><0.1; **<i>P</i><0.05 (Student’s <i>t</i>-test). AA, ambient air; O₃, elevated ozone; Sasa, Sasanishiki; Haba, Habataki. (C) Typical panicles of Habataki grown under ambient air (left) or elevated ozone (right). Yellow circles indicateidentify each primary rachis branches. Scale bar = 5 cm.</p

Wavelength dependency of the light-driven transcriptional activation of the cucumber CPD photolyase gene ( Conference Paper )

UVB radiation (280 nm ∼ 315 nm) is known to retard plant growth. DNA lesions are thought to be largely responsible for the growth inhibition due to UVB. Cyclobutane pyrimidine dimers (CPDs) constitute a major portion of UVB-induced DNA lesions. CPD-specific DNA photolyase (CPD photolyase) rapidly restores CPDs, rendering plants tolerant to UVB. We previously showed that the photolyase activity in cucumber leaves rises in the midst of the day when the solar UVB is intense, and that such diurnal fluctuation of the photolyase activity is attributable principally to light-dependent transcriptional activation of the CPD photolyase gene (CsPHR). In the present research, we examined the accumulation of the CsPHR transcripts under monochromatic light and showed that the CsPHR transcription is maximally induced by UVB with wavelengths around 310nm. It was surmised that the transcriptional activation is mediated by an unidentified UVB-specific photoreceptor