The major‐effect quantitative trait locus CsARN6.1 encodes an AAA ATPase domain‐containing protein that is associated with waterlogging stress tolerance by promoting adventitious root formation

In plants, the formation of hypocotyl‐derived adventitious roots (ARs) is an important morphological acclimation to waterlogging stress; however, its genetic basis remains fragmentary. Here, through combined use of bulked segregant analysis‐based whole‐genome sequencing, SNP haplotyping and fine genetic mapping, we identified a candidate gene for a major‐effect QTL, ARN6.1, that was responsible for waterlogging tolerance due to increased AR formation in the cucumber line Zaoer‐N. Through multiple lines of evidence, we show that CsARN6.1 is the most possible candidate for ARN6.1 which encodes an AAA ATPase. The increased formation of ARs under waterlogging in Zaoer‐N could be attributed to a non‐synonymous SNP in the coiled‐coil domain region of this gene. CsARN6.1 increases the number of ARs via its ATPase activity. Ectopic expression of CsARN6.1 in Arabidopsis resulted in better rooting ability and lateral root development in transgenic plants. Transgenic cucumber expressing the CsARN6.1^Asp allele from Zaoer‐N exhibited a significant increase in number of ARs compared with the wild type expressing the allele from Pepino under waterlogging conditions. Taken together, these data support that the AAA ATPase gene CsARN6.1 has an important role in increasing cucumber AR formation and waterlogging tolerance.     

Dehydration-regulated processing of late embryogenesis abundant protein in a desiccation-tolerant nematode

Late embryogenesis abundant (LEA) proteins occur in desiccation-tolerant organisms, including the nematode Aphelenchus avenae, and are thought to protect other proteins from aggregation. Surprisingly, expression of the LEA protein AavLEA1 in A. avenae is partially discordant with that of its gene: protein is present in hydrated animals despite low cognate mRNA levels. Moreover, on desiccation, when its gene is upregulated, AavLEA1 is specifically cleaved to discrete, smaller polypeptides. A processing activity was found in protein extracts of dehydrated, but not hydrated, nematodes, and main cleavage sites were mapped to 11-mer repeated motifs in the AavLEA1 sequence. Processed polypeptides retain function as protein anti-aggregants and we hypothesise that the expression pattern and cleavage of LEA protein allow rapid, maximal availability of active molecules to the dehydrating animal.     

胚胎晚期富集蛋白与生物的干旱胁迫耐受性

胚胎晚期富集蛋白(Late embryogenesis abundant,LEA)是参与生物体抵抗干旱胁迫的一类重要蛋白。LEA蛋白可分为7组。大多数LEA蛋白具有亲水性及热稳定性。LEA蛋白在水溶液中通常为无折叠状态,但脱水胁迫可诱导其转变为α-螺旋。近年来关于LEA蛋白的研究取得了较多进展。研究结果表明LEA蛋白可定位于细胞内的多种细胞器中,且LEA蛋白可能具有多重保护作用,如保护蛋白质及酶活性、或保护细胞的膜结构、或具有抗氧化作用、结合离子或保护DNA等。以下主要介绍了LEA蛋白的功能、二级结构及保护作用机制。     

A mitochondrial late embryogenesis abundant protein stabilizes model membranes in the dry state

Late embryogenesis abundant (LEA) proteins are a highly diverse group of polypeptides expected to play important roles in desiccation tolerance of plant seeds. They are also found in other plant tissues and in some anhydrobotic invertebrates, fungi, protists and prokaryotes. The LEA protein LEAM accumulates in the matrix space of pea (Pisum sativum) mitochondria during late seed maturation. LEAM is an intrinsically disordered protein folding into amphipathic α-helix upon desiccation. This suggests that it could interact with the inner mitochondrial membrane, providing structural protection in dry seeds. Here, we have used Fourier-transform infrared and fluorescence spectroscopy to gain insight into the molecular details of interactions of LEAM with phospholipid bilayers in the dry state and their effects on liposome stability. LEAM interacted specifically with negatively charged phosphate groups in dry phospholipids, increasing fatty acyl chain mobility. This led to an enhanced stability of liposomes during drying and rehydration, but also upon freezing. Protection depended on phospholipid composition and was strongly enhanced in membranes containing the mitochondrial phospholipid cardiolipin. Collectively, the results provide strong evidence for a function of LEAM as a mitochondrial membrane protectant during desiccation and highlight the role of lipid composition in the interactions between LEA proteins and membranes.     

The in vitro structure and functions of the disordered late embryogenesis abundant three proteins

Late embryogenesis abundant (LEA) proteins are produced during seed embryogenesis and in vegetative tissue in response to various abiotic stressors. A correlation has been established between LEA expression and stress tolerance, yet their precise biochemical mechanism remains elusive. LEA proteins are very rich in hydrophilic amino acids, and they have been found to be intrinsically disordered proteins (IDPs) in vitro. Here, we perform biochemical and structural analyses of the four LEA3 proteins from Arabidopsis thaliana (AtLEA3). We show that the LEA3 proteins are disordered in solution but have regions with propensity for order. All LEA3 proteins were effective cryoprotectants of LDH in the freeze/thaw assays, while only one member, AtLEA3‐4, was shown to bind Cu²⁺ and Fe³⁺ ions with micromolar affinity. As well, only AtLEA3‐4 showed binding and a gain in α‐helicity in the presence of the membrane mimic dodecylphosphocholine (DPC). We explored this interaction in greater detail using ¹⁵N‐heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance, and demonstrate that two sets of conserved motifs present in AtLEA3‐4 are involved in the interaction with the DPC micelles, which themselves gain α‐helical structure.     

<Emphasis Type="Italic">OsLEA3</Emphasis>, a late embryogenesis abundant protein gene from rice,confers tolerance to water deficit and salt stress to transgenic rice

OsLEA3 is a late embryogenesis abundant group 3 protein. The OsLEA3 gene located on chromosome 5 of rice (Oryza sativa L.) includes one intron and two exons and encodes a protein of 200 amino acid residues. Expression analysis revealed that OsLEA3 was induced by water deficit and salt stress. Overexpression of the OsLEA3 gene in the transgenic rice plants allowed us to test the role of the OsLEA3 protein in stress tolerance. The accumulation of the OsLEA3 protein in the vegetative tissues of transgenic rice plants enhanced their tolerance to water deficit and salt stress. These results demonstrate a role for the OsLEA3 protein in stress protection and suggest the potential of the OsLEA3 gene for genetic engineering of stress tolerance.     

Identification of a stable quantitative trait locus for percentage grains with white chalkiness in rice (Oryza sativa)

High chalkiness is a major problem in many rice-producing areas of the world, especially in hybrid rice (Oryza sativa L.) in China. We previously showed a major quantitative trait locus for the percentage of grains with white chalkiness (QTLqPGWC-8) in the interval G1149-R727 on chromosome 8 using a chromosome segment substitution line (CSSL). Here, we selected the line-CSSL50 harboring the QTLqPGWC-8 allele from the CSSLs derived from a cross between Asominori (as a recurrent parent) and IR24 (as a donor parent), which had higher percentage chalkiness, markedly different from that of Asominori. There were also significant differences in starch granules, appearance of amylose content (AAC) and milling qualities between Asominori and CSSL50, but not in grain size or thousand grain weight (TGW). The BC(4) F(2) and BC(4) F(3) populations from a cross between CSSL50 and Asominori were used for fine mapping of qPGWC-8. We narrowed down the location of this QTL to a 142 kb region between Indel markers 8G-7 and 8G-9. QTLqPGWC-8 accounted for 50.9% of the difference in PGWC between the parents. The markers tightly linked to qPGWC-8 should facilitate cloning of the gene underlying this QTL and will be of value for marker-assisted selection in breeding rice varieties with better grain quality.     

The effect of salt and temperature on the conformational changes of P1LEA‐22, a repeat unit of plant Late Embryogenesis Abundant proteins

The effect of choline chloride on the conformational dynamics of the 11‐mer repeat unit P1LEA‐22 of group 3 Late Embryogenesis Abundant (G3LEA) proteins was studied. Circular dichroism data of aqueous solutions of P1LEA‐22 revealed that the peptide favors a polyproline II (PPII) helix structure at low temperature, with increasing temperature promoting a gain of unstructured conformations. Furthermore, increases in sample FeCl₃ or choline chloride concentrations causes a gain in PPII helical structure at low temperature. The potential role of PPII structure in intrinsically disordered and G3LEA proteins is discussed, including its ability to easily access other secondary structural conformations such as α‐helix and β‐sheet, which have been observed for dehydrated G3LEA proteins. The observed effect of FeCl₃ and choline chloride salts on P1LEA‐22 suggests favorable cation interactions with the PPII helix, supporting ion sequestration as a G3LEA protein function. As choline chloride is suggested to improve salt tolerance and protect cell membrane in plants at low temperature, our results support adoption of the PPII structure as a possible damage‐preventing measure of Late Embryogenesis Abundant proteins.