Role of CIPK6 in root growth and auxin transport

The calcium signaling module CaM-IQM destabilizes IAA-ARF interaction to regulate callus and lateral root formation

Induction of a pluripotent cell mass, called callus, from detached organs is an initial step in in vitro plant regeneration, during which phytohormone auxin-induced ectopic activation of a root developmental program has been shown to be required for subsequent de novo regeneration of shoots and roots. However, whether other signals are involved in governing callus formation, and thus plant regeneration capability, remains largely unclear. Here, we report that the Arabidopsis calcium (Ca²⁺) signaling module CALMODULIN IQ-MOTIF CONTAINING PROTEIN (CaM-IQM) interacts with auxin signaling to regulate callus and lateral root formation. We show that disruption of IQMs or CaMs retards auxin-induced callus and lateral root formation by dampening auxin responsiveness, and that CaM-IQM complexes physically interact with the auxin signaling repressors INDOLE-3-ACETIC ACID INDUCIBLE (IAA) proteins in a Ca²⁺-dependent manner. We further provide evidence that the physical interaction of CaM6 with IAA19 destabilizes the repressive interaction of IAA19 with AUXIN RESPONSE FACTOR 7 (ARF7), and thus regulates auxin-induced callus formation. These findings not only define a critical role of CaM-IQM-mediated Ca²⁺ signaling in callus and lateral root formation, but also provide insight into the interplay of Ca²⁺ signaling and auxin actions during plant regeneration and development.

Ectopic expression of BdCIPK31 confers enhanced low-temperature tolerance in transgenic tobacco plants

Calcineurin B-like protein (CBL), the Ca2+ sensor, and its interacting protein kinases (CIPKs) play essential roles in plants' response to stress. However, few studies have focused on the functions of CIPKs in low-temperature response. In the present study, BdCIPK31, a cold-responsive CIPK in Brachypodium distachyon, was found to participate in low-temperature response. Ectopic expression of BdCIPK31 conferred cold tolerance in transgenic tobaccos. Further analyses indicated that expression of BdCIPK31 improved ROS detoxication and omsoprotectant biosynthesis in transgenic plants under low-temperature treatment, suggesting that the BdCIPK31 functions positively in plant adaption to the cold-induced oxidative and osmotic stresses. Moreover, BdCIPK31 could upregulate the expressions of some representative stress-related genes under cold stress. In conclusion, these findings suggest that BdCIPK31 functions positively in plant cold response.

Characterization of the cork oak transcriptome dynamics during acorn development

BACKGROUND

Cork oak (Quercus suber L.) has a natural distribution across western Mediterranean regions and is a keystone forest tree species in these ecosystems. The fruiting phase is especially critical for its regeneration but the molecular mechanisms underlying the biochemical and physiological changes during cork oak acorn development are poorly understood. In this study, the transcriptome of the cork oak acorn, including the seed, was characterized in five stages of development, from early development to acorn maturation, to identify the dominant processes in each stage and reveal transcripts with important functions in gene expression regulation and response to water.

RESULTS

A total of 80,357 expressed sequence tags (ESTs) were de novo assembled from RNA-Seq libraries representative of the several acorn developmental stages. Approximately 7.6 % of the total number of transcripts present in Q. suber transcriptome was identified as acorn specific. The analysis of expression profiles during development returned 2,285 differentially expressed (DE) transcripts, which were clustered into six groups. The stage of development corresponding to the mature acorn exhibited an expression profile markedly different from other stages. Approximately 22 % of the DE transcripts putatively code for transcription factors (TF) or transcriptional regulators, and were found almost equally distributed among the several expression profile clusters, highlighting their major roles in controlling the whole developmental process. On the other hand, carbohydrate metabolism, the biological pathway most represented during acorn development, was especially prevalent in mid to late stages as evidenced by enrichment analysis. We further show that genes related to response to water, water deprivation and transport were mostly represented during the early (S2) and the last stage (S8) of acorn development, when tolerance to water desiccation is possibly critical for acorn viability.

CONCLUSIONS

To our knowledge this work represents the first report of acorn development transcriptomics in oaks. The obtained results provide novel insights into the developmental biology of cork oak acorns, highlighting transcripts putatively involved in the regulation of the gene expression program and in specific processes likely essential for adaptation. It is expected that this knowledge can be transferred to other oak species of great ecological value.

Maize LAZY1 mediates shoot gravitropism and inflorescence development through regulating auxin transport, auxin signaling, and light response

Auxin is a plant hormone that plays key roles in both shoot gravitropism and inflorescence development. However, these two processes appear to be parallel and to be regulated by distinct players. Here, we report that the maize (Zea mays) prostrate stem1 mutant, which is allelic to the classic mutant lazy plant1 (la1), displays prostrate growth with reduced shoot gravitropism and defective inflorescence development. Map-based cloning identified maize ZmLA1 as the functional ortholog of LAZY1 in rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana). It has a unique role in inflorescence development and displays enriched expression in reproductive organs such as tassels and ears. Transcription of ZmLA1 responds to auxin and is repressed by light. Furthermore, ZmLA1 physically interacts with a putative auxin transport regulator in the plasma membrane and a putative auxin signaling protein in the nucleus. RNA-SEQ data showed that dozens of auxin transport, auxin response, and light signaling genes were differentially expressed in la1 mutant stems. Therefore, ZmLA1 might mediate the cross talk between shoot gravitropism and inflorescence development by regulating auxin transport, auxin signaling, and probably light response in maize.

Molecular cloning and functional characterization of a novel apple MdCIPK6L gene reveals its involvement in multiple abiotic stress tolerance in transgenic plants

CBL-interacting protein kinases (CIPKs) are involved in many aspects of plant responses to abiotic stresses. However, their functions are poorly understood in fruit trees. In this study, a salt-induced MdCIPK6L gene was isolated from apple. Its expression was positively induced by abiotic stresses, stress-related hormones and exogenous Ca(2+). MdCIPK6L was not homologous to AtSOS2, however, its ectopic expression functionally complemented Arabidopsis sos2 mutant. Furthermore, yeast two-hybrid assay showed that MdCIPK6L protein interacted with AtSOS3, indicating that it functions in salt tolerance partially like AtSOS2 through SOS pathway. As a result, the overexpression of both MdCIPK6L and MdCIPK6LT175D remarkably enhanced the tolerance to salt, osmotic/drought and chilling stresses, but did not affect root growth, in transgenic Arabidopsis and apple. Also, T-to-D mutation to MdCIPK6L at Thr175 did not affect its function. These differences between MdCIPK6L and other CIPKs, especially CIPK6s, indicate that MdCIPK6L encodes a novel CIPK in apple. Finally, MdCIPK6L overexpression also conferred tolerance to salt, drought and chilling stresses in transgenic tomatoes. Therefore, MdCIPK6L functions in stress tolerance crossing the species barriers, and is supposed to be a potential candidate gene to improve stress tolerance by genetic manipulation in apple and other crops.

Molecular cloning and functional characterization of MdSOS2 reveals its involvement in salt tolerance in apple callus and Arabidopsis

Plants respond to various environmental stresses by activating "stress genes". CIPKs (CBL-interacting protein kinases) family genes play an important role in the process of stress response. In this study, a CIPK gene MdSOS2 was isolated from apple (Malus × Domestica). Sequence alignment and phylogenetic analysis showed that it is highly similar with Arabidopsis AtSOS2 and contained the conserved domains and motifs. Expression analysis demonstrated that MdSOS2 expressed in all tested organs at different levels, and positively in response to salt stress. Furthermore, the ectopic expression of MdSOS2 complemented the function of Arabidopsis sos2 mutant, and conferred enhanced salt tolerance to the transgenic Arabidopsis. Yeast two-hybrid assay indicated that the N-terminal of MdSOS2 protein physically interacted with MdSOS3 and AtSOS3, respectively, suggesting that SOS pathway operates in apple tree. Finally, MdSOS2 overexpression enhanced, while its suppression reduced the tolerance to salt in transgenic apple calluses, indicating that MdSOS2 acts as a positive regulator in response to salt stress in apple.

Transcriptome analysis reveals salt-stress-regulated biological processes and key pathways in roots of cotton (Gossypium hirsutum L.)

High salinity is one of the main factors limiting cotton growth and productivity. The genes that regulate salt stress in TM-1 upland cotton were monitored using microarray and real-time PCR (RT-PCR) with samples taken from roots. Microarray analysis showed that 1503 probe sets were up-regulated and 1490 probe sets were down-regulated in plants exposed for 3h to 100mM NaCl, and RT-PCR analysis validated 42 relevant/related genes. The distribution of enriched gene ontology terms showed such important processes as the response to water stress and pathways of hormone metabolism and signal transduction were induced by the NaCl treatment. Some key regulatory gene families involved in abiotic and biotic sources of stress such as WRKY, ERF, and JAZ were differentially expressed. Our transcriptome analysis might provide some useful insights into salt-mediated signal transduction pathways in cotton and offer a number of candidate genes as potential markers of tolerance to salt stress.