Application of T-DNA activation tagging to identify glutamate receptor-like genes that enhance drought tolerance in plants

Key message

A high-quality rice activation tagging population has been developed and screened for drought-tolerant lines using various water stress assays. One drought-tolerant line activated two rice glutamate receptor-like genes. Transgenic overexpression of the rice glutamate receptor-like genes conferred drought tolerance to rice and Arabidopsis.

Abstract

Rice (Oryza sativa) is a multi-billion dollar crop grown in more than one hundred countries, as well as a useful functional genetic tool for trait discovery. We have developed a population of more than 200,000 activation-tagged rice lines for use in forward genetic screens to identify genes that improve drought tolerance and other traits that improve yield and agronomic productivity. The population has an expected coverage of more than 90 % of rice genes. About 80 % of the lines have a single T-DNA insertion locus and this molecular feature simplifies gene identification. One of the lines identified in our screens, AH01486, exhibits improved drought tolerance. The AH01486 T-DNA locus is located in a region with two glutamate receptor-like genes. Constitutive overexpression of either glutamate receptor-like gene significantly enhances the drought tolerance of rice and Arabidopsis, thus revealing a novel function of this important gene family in plant biology.     

AtHSP17.8 overexpression in transgenic lettuce gives rise to dehydration and salt stress resistance phenotypes through modulation of ABA-mediated signaling

Key message

Transgenic Arabidopsis and lettuce plants overexpressing AtHSP17.8 showed ABA-hypersensitive but abiotic stress-resistant phenotypes. ABA treatment caused a dramatic induction of early ABA-responsive genes in AtHSP17.8 -overexpressing transgenic lettuce.

Abstract

Plant small heat shock proteins function as chaperones in protein folding. In addition, they are involved in responses to various abiotic stresses, such as dehydration, heat and high salinity in Arabidopsis. However, it remains elusive how they play a role in the abiotic stress responses at the molecular level. In this study, we provide evidence that Arabidopsis HSP17.8 (AtHSP17.8) positively regulates the abiotic stress responses by modulating abscisic acid (ABA) signaling in Arabidopsis, and also in lettuce, a heterologous plant when ectopically expressed. Overexpression of AtHSP17.8 in both Arabidopsis and lettuce leads to hypersensitivity to ABA and enhanced resistance to dehydration and high salinity stresses. Moreover, early ABA-responsive genes, ABI1, ABI5, NCED3, SNF4 and AREB2, were rapidly induced in AtHSP17.8-overexpressing transgenic Arabidopsis and lettuce. Based on these data, we propose that AtHSP17.8 plays a crucial role in abiotic stress responses by positively modulating ABA-mediated signaling in both Arabidopsis and lettuce. Moreover, our results suggest that stress-tolerant lettuce can be engineered using the genetic and molecular resources of Arabidopsis.     

Overexpression of a novel salt stress-induced glycine-rich protein gene from alfalfa causes salt and ABA sensitivity in Arabidopsis

Key message

We cloned a novel salt stress-induced glycine-rich protein gene ( MsGRP ) from alfalfa. Its overexpression retards seed germination and seedling growth of transgenic Arabidopsis after salt and ABA treatments.

Abstract

Since soil salinity is one of the most significant abiotic stresses, salt tolerance is required to overcome salinity-induced reductions in crop productivity. Many glycine-rich proteins (GRPs) have been implicated in plant responses to environmental stresses, but the function and importance of some GRPs in stress responses remain largely unknown. Here, we report on a novel salt stress-induced GRP gene (MsGRP) that we isolated from alfalfa. Compared with some glycine-rich RNA-binding proteins, MsGRP contains no RNA recognition motifs and localizes in the cell membrane or cell wall according to the subcellular localization result. MsGRP mRNA is induced by salt, abscisic acid (ABA), and drought stresses in alfalfa seedlings, and its overexpression driven by a constitutive cauliflower mosaic virus-35S promoter in Arabidopsis plants confers salinity and ABA sensitivity compared with WT plants. MsGRP retards seed germination and seedling growth of transgenic Arabidopsis plants after salt and ABA treatments, which implies that MsGRP may affect germination and growth through an ABA-dependent regulation pathway. These results provide indirect evidence that MsGRP plays important roles in seed germination and seedling growth of alfalfa under some abiotic stress conditions.     

Carbon assimilation variation and control in Picea rubens,Picea mariana,and their hybrids under ambient and elevated CO2

Key message

After 3 years of CO ₂ treatments, A stimulation from ambient to elevated CO ₂ was strongly related to the total dry mass change (%), supporting the sink demand A hypothesis.

Abstract

Adaptations related to gas exchange are important fitness traits in plants and have significant growth and ecological implications. Assimilation (A) and assimilation to internal CO₂ (AC _i ) response curve parameters were quantified from a red spruce (RS) (Picea rubens Sarg.)—black spruce (BS) [P. mariana (Mill.) B.S.P.] controlled-cross hybrid complex grown under ambient and elevated CO₂ conditions. Under ambient conditions, maximum A (A _max), maximum rate of carboxylation by rubisco (V _cmax), maximum rate of electron transport (J _max), and carboxylation efficiency (CE) generally increased with increasing BS content; however, under elevated CO₂ conditions, hybrid index 50 (hybrid index number is the percentage of RS, balance BS) often had greater values than the other indices. There were significant hybrid index, CO₂, and hybrid index × CO₂ effects for A _growth at 360 ppm (A ₃₆₀) and 720 ppm (A ₇₂₀). The net A stimulation (A _stim), from ambient to elevated CO₂ treatment after 3 years was 10.8, 57.8, 74.1, 69.8, and 58.7 %, for hybrid indices 0 (BS), 25, 50, 75, and 100 (RS), respectively. Why does BS have the least A _stim, hybrid index 50 the most, and RS a moderate level? There was a significant relationship between A ₃₆₀ and ambient total biomass among indices (P = 0.096), but none was found between A ₇₂₀ and elevated total biomass. However, A _stim (%) was strongly related to the change in total dry mass (%) in response to elevated CO₂ (R ² = 0.931, P = 0.008), supporting the hypothesis that sink demand drives A. Traits A _max, V _cmax and J _max were correlated to total chlorophyll concentration. Moreover, A _max V _cmax and J _max also showed a significant underlying male effect, particularly under ambient conditions consistent with the paternal inheritance of the chloroplast genome.     

New names,combinations, and lectotypifications in Heterotheca (Compositae: Astereae)

The following new names and combinations are proposed:Heterotheca barbata (Rydb.) Semple,H. horrida subsp.cinerascens (S. F. Blake) Semple,H. fulcrata vararizonica Semple,H. fulcrata var.senilis (Wooton & Standley) Semple,H. oregona var.compacta (Keck) Semple,H. oregona var.rudis (Greene) Semple,H. oregona var.scaberrima (A. Gray) Semple,H. pumila (Greene) Semple,H. villosa var.pedunculata (Greene) V. Harms ex Semple, andH. zionensis Semple. The following chromosome numbers are reported for the first time:H. fulcrata var.arizonica, 2n=9 _II ;H. horrida subsp.cinerascens, 2n=18 _II ;H. pumila, 2n=9 _II ,2n=18 _II ;H. zionensis, 2n=9 _II .