The Arabidopsis LOS5/ABA3 locus encodes a molybdenum cofactor sulfurase and modulates cold stress- and osmotic stress-responsive gene expression

The ankyrin repeat-containing protein MdANK2B regulates salt tolerance and ABA sensitivity in Malus domestica

The ankyrin repeat-containing protein MdANK2B was identified to contribute to increasing resistance to salt stress and decreasing sensitivity to ABA in Malus domestica. Ankyrin (ANK) repeat-containing proteins occur widely in prokaryotes, eukaryotes, and even in some viruses and play a critical role in plant growth and development, as well as the response to biotic and abiotic stress. However, the function of ANK repeat-containing proteins in apple (Malus domestica) has not yet been investigated. Here, we identified apple MdANK2B based on homology analysis with the Arabidopsis ANK repeat-containing proteins AtAKR2A and AtAKR2B. MdANK2B was found to be localized in the cytoplasm, and its encoding gene was highly expressed in both apple leaves and fruits. In addition, MdANK2B gene expression was highly induced by salt stresses and abscisic acid (ABA). Overexpression of MdANK2B increased resistance to salt stress and decreased sensitivity to ABA in both transgenic apple calli and seedlings. In addition, overexpression of MdANK2B reduced the accumulation of reactive oxygen species (ROS) by enhancing the activity of antioxidant enzymes in response to salt stress. Our data revealed the role of MdANK2B in response to salt stress and ABA treatment in apple, which widens the known functions of ANK repeat-containing proteins in response to abiotic stress.

Whole organ, venation and epidermal cell morphological variations are correlated in the leaves of Arabidopsis mutants

Despite the large number of genes known to affect leaf shape or size, we still have a relatively poor understanding of how leaf morphology is established. For example, little is known about how cell division and cell expansion are controlled and coordinated within a growing leaf to eventually develop into a laminar organ of a definite size. To obtain a global perspective of the cellular basis of variations in leaf morphology at the organ, tissue and cell levels, we studied a collection of 111 non-allelic mutants with abnormally shaped and/or sized leaves, which broadly represent the mutational variations in Arabidopsis thaliana leaf morphology not associated with lethality. We used image-processing techniques on these mutants to quantify morphological parameters running the gamut from the palisade mesophyll and epidermal cells to the venation, whole leaf and rosette levels. We found positive correlations between epidermal cell size and leaf area, which is consistent with long-standing Avery's hypothesis that the epidermis drives leaf growth. In addition, venation parameters were positively correlated with leaf area, suggesting that leaf growth and vein patterning share some genetic controls. Positional cloning of the genes affected by the studied mutations will eventually establish functional links between genotypes, molecular functions, cellular parameters and leaf phenotypes.

Plant U-box armadillo repeat proteins AtPUB18 and AtPUB19 are involved in salt inhibition of germination in Arabidopsis

Plant U-box armadillo repeat (PUB-ARM) proteins represent a type of E3 ubiquitin ligase. PUB-ARM proteins have various functions in plant development, plant defence and plant stress responses. The so far uncharacterised PUB-ARM proteins AtPUB18 and AtPUB19 are highly homologous to each other and regulated on the transcript level by ABA and NaCl. To investigate their physiological function, we isolated and characterised two Arabidopsis mutants and named them pub18-1 and pub19-1. However, these single mutants did not show any ABA- or salt-dependent phenotype. In contrast, pub18-1/pub19-1 double mutant seeds were less sensitive to ABA and NaCl inhibition of seed germination compared to wild-type seeds, indicating that both PUB-ARM proteins may coordinately function as regulatory components in ABA or salt inhibition of germination.

Mutations of the silkworm molybdenum cofactor sulfurase gene, og, cause translucent larval skin

Normal silkworms (Bombyx mori) have opaque larval skin due to uric acid accumulation in the epidermis while a mutant, og, is translucent owing to a deficiency in xanthine dehydrogenase (XDH), which synthesizes uric acid. Molybdenum cofactor (MoCo) sulfurase is responsible for XDH activation in various organisms. A silkworm MoCo sulfurase gene was cloned and found to be on the og locus, whose mutant alleles, og(k) and og(t), show premature stop codons, proving that og is the MoCo sulfurase gene. It was observed that a miniature inverted-repeat transposable element (MITE), named Organdy, when inserted in an og(t) mutant allele exon, causes unstable splicing of a downstream intron leading to incomplete open reading frames.