Abscisic acid (ABA) plays an essential role in seed germination. In this study, we demonstrate that one SNF1-RELATED PROTEIN KINASE3-type protein kinase, SOS2-LIKE PROTEIN KINASE5 (PKS5), is involved in ABA signal transduction via the phosphorylation of an interacting protein, ABSCISIC ACID-INSENSITIVE5 (ABI5). We found that pks5-3 and pks5-4, two previously identified PKS5 superactive kinase mutants with point mutations in the PKS5 FISL/NAF (a conserved peptide that is necessary for interaction with SOS3 or SOS3-LIKE CALCIUM BINDING PROTEINs) motif and the kinase domain, respectively, are hypersensitive to ABA during seed germination. PKS5 was found to interact with ABI5 in yeast (Saccharomyces cerevisiae), and this interaction was further confirmed in planta using bimolecular fluorescence complementation. Genetic studies revealed that ABI5 is epistatic to PKS5. PKS5 phosphorylates a serine (Ser) residue at position 42 in ABI5 and regulates ABA-responsive gene expression. This phosphorylation was induced by ABA in vivo and transactivated ABI5. Expression of ABI5, in which Ser-42 was mutated to alanine, could not fully rescue the ABA-insensitive phenotypes of the abi5-8 and pks5-4abi5-8 mutants. In contrast, mutating Ser-42 to aspartate rescued the ABA insensitivity of these mutants. These data demonstrate that PKS5-mediated phosphorylation of ABI5 at Ser-42 is critical for the ABA regulation of seed germination and gene expression in Arabidopsis (Arabidopsis thaliana).

bZIP (basic leucine zipper) transcription factors coordinate plant growth and development and control responses to environmental stimuli. The genome of Chinese cabbage (Brassica rapa) encodes 136 putative bZIP transcription factors. The bZIP transcription factors in Brassica rapa (BrbZIP) are classified into 10 subfamilies. Phylogenetic relationship analysis reveals that subfamily A consists of 23 BrbZIPs. Two BrbZIPs within subfamily A, Bra005287 and Bra017251, display high similarity to ABI5 (ABA Insensitive 5). Expression of subfamily A BrbZIPs, like BrABI5a (Bra005287/BrbZIP14) and BrABI5b (Bra017251/BrbZIP13), are significantly induced by the plant hormone ABA. Subcellular localization assay reveal that both BrABI5a and BrABI5b have a nuclear localization. BrABI5a and BrABI5b could directly stimulate ABA Responsive Element-driven HIS (a HIS3 reporter gene, which confers His prototrophy) or LUC (LUCIFERASE) expression in yeast and Arabidopsis protoplast. Deletion of the bZIP motif abolished BrABI5a and BrABI5b transcriptional activity. The ABA insensitive phenotype of Arabidopsis abi5-1 is completely suppressed in transgenic lines expressing BrABI5a or BrABI5b. Overall, these results suggest that ABI5 orthologs, BrABI5a and BrABI5b, have key roles in ABA signalling in Chinese cabbage.

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In July 2010, cacti with typical phytoplasma symptoms were observed in Yangling district, Shaanxi Province, China. Based on amplification of 16S rRNA gene, phytoplasmas were detected by polymerase chain reaction (PCR) driven with universal primer pairs P1/ P7, followed by a nested PCR with universal primer pairs R16F2n⁄R16R2. Fragments of expected sizes (1.8 kb and 1.2 kb) were obtained from symptomatic samples, but not from the asymptomatic samples. Sequencing results and BLASTn analysis of the 1806 bp products (P1/P7) showed that the phytoplasma belonged to group 16SrII. Phylogenetic analysis to the R16F2n⁄R16R2 region and virtual restriction fragment length polymorphism (RFLP) indicated that this phytoplasma was a member of subgroup 16SrII-C. This is the first reported occurrence of a peanut witches'-broom phytoplasma infecting plants in northern areas of China.

In July 2010, symptoms suggestive of phytoplasma infection were observed on Rose Balsam (Impatiens balsamina) around Yangling, China. Nested polymerase chain reaction with universal 16S rDNA phytoplasma primers P1⁄P6 and R16F2n⁄R16R2 yielded amplicons of expected size (1.2 kb) from all symptomatic, but not asymptomatic, leaf samples. Sequencing results and NCBI BLASTn analysis of the 1246 bp products (R16F2n⁄R16R2) showed that the phytoplasma belonged to group 16SrI. Restriction fragment length polymorphism and phylogenetic analysis showed the phytoplasma had a close relationship to subgroup 16SrI-D. This is the first report of a phytoplasma infecting Rose Balsam.