SQUAMOSA Promoter-Binding Protein-Like (SPL) genes encode plant-specific transcription factors that play important roles in plant phase transition, flower and fruit development, plant architecture, gibberellins signaling, sporogenesis, and response to copper and fungal toxins. In Arabidopsis, many SPL genes are post-transcriptionally regulated by the microRNA (miRNA) miR156, among which AtSPL9 in turn positively regulates the expression of the second miRNA miR172. This miR156-AtSPL9-miR172 regulatory pathway plays critical roles during juvenile to adult leaf development and the miR156-SPLs feedback interaction persists all through the plant development, which may be conserved in other plants. In the present paper, we provide a concise review on the most recent progress in the regulatory mechanisms associated with plant SPL transcription factors, especially in relation to miRNAs. The potential application of these discoveries in agriculture is briefly discussed.

Calcium-dependent protein kinases (CDPKs) are crucial sensors of calcium concentration changes in plant cells under diverse endogenous and environmental stimuli. We identified 20 CDPK genes from bread wheat and performed a comprehensive study on their structural, functional and evolutionary characteristics. Full-length cDNA sequences of 14 CDPKs were obtained using various approaches. Wheat CDPKs were found to be similar to their counterparts in rice in genomic structure, GC content, subcellular localization, and subgroup classification. Divergence time estimation of wheat CDPK gene pairs and wheat-rice orthologs suggested that most duplicated genes already existed in the common ancestor of wheat and rice. The number of CDPKs in diploid wheat genome was estimated to be at least 26, a number close to that in rice, Arabidopsis, and poplar. However, polymorphism among EST sequences uncovered transcripts of all three homoeologous alleles for 13 out of 20 CDPKs. Thus, the hexaploid wheat should have 2-3 fold more CDPK genes expressing in their cells than the diploid species. Wheat CDPK genes were found to respond to various biotic and abiotic stimuli, including cold, hydrogen peroxide (H(2)O(2)), salt, drought, powdery mildew (Blumeria graminis tritici, Bgt), as well as phytohormones abscisic acid (ABA) and gibberellic acid (GA). Each CDPK gene often responded to multiple treatments, suggesting that wheat CDPKs are converging points for multiple signal transduction pathways. The current work represents the first comprehensive study of CDPK genes in bread wheat and provides a foundation for further functional study of this important gene family in Triticeae.

Branching is an important trait of plant development regulated by environmental signals. Phytochromes in Arabidopsis mediate branching in response to the changes in the red light:far-red light ratio (R:FR), the mechanisms of which are still elusive. Here it is shown that overexpression of CONSTANS-LIKE 7 (COL7) results in an abundant branching phenotype which could be efficiently suppressed by shade or a simulated shade environment (low R:FR). Moreover, col7 mutants develop shorter hypocotyls and COL7 overexpression lines develop longer hypocotyls in comparison with the wild type in low R:FR, indicating that COL7 acts as an enhancer of the shade avoidance response. In shade or transient low R:FR, transcriptional and post-transcriptional expression levels of COL7 are up-regulated and positively associated with rapid mRNA accumulation of PHYTOCHROME INTERACTING FACTOR 3-LIKE 1 (PIL1), a marker gene of shade avoidance syndrome (SAS). Taken together, the results suggest a dual role for COL7 which promotes branching in high R:FR conditions but enhances SAS in low R:FR conditions.

The NAC family is one of the largest families of plant-specific transcription factors (TFs) and NAC proteins play important regulatory roles in a variety of developmental and stress response processes in plants. Members of the NAC family TFs have been shown to be important regulators of leaf senescence in a number of plant species. Here we report the identification of the NAC family in tobacco (Nicotiana tabacum) and characterization of the potential role of some of the tobacco NAC TFs in regulating leaf senescence. A total of 154 NAC genes (NtNACs) were identified and clustered together with the Arabidopsis NAC family into fifteen groups (a-o). Transcriptome data analysis followed by qRT-PCR validation showed that the majority of the senescence-up-regulated NtNACs fall into subgroups NAC-b and f. A number of known senescence regulators from Arabidopsis also belong to these two subgroups. Among these senescence-up-regulated NtNACs, NtNAC080, a close homolog of AtNAP, is a positive regulator of leaf senescence. Overexpression of NtNAC080 caused early senescence in Arabidopsis leaves and NtNAC080 mutation induced by Cas9/gRNA in tobacco led to delayed leaf senescence.

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Arabidopsis phytochrome B (phyB) is the major photoreceptor that senses the ratio of red to far-red light (R:FR) to regulate the shade-avoidance response (SAR). It has been hypothesized that altered homeostasis of phytohormones such as auxin and strigolactone is at least partially responsible for SAR, but the mechanism underlying phyB regulation of the hormonal change is not fully understood. Previously we reported that CONSTANS-LIKE 7 (COL7) enhances branching number under high R:FR but not under low R:FR, implying that COL7 may be involved in the phyB-mediated SAR. In this study, we provide evidence that COL7 reduces auxin levels in a high R:FR-dependent manner. We found that the phyB mutation suppresses the COL7-induced branching proliferation. Moreover, COL7 promotes mRNA expression of SUPERROOT 2 (SUR2), which encodes a suppressor of auxin biosynthesis, in high R:FR but not in low R:FR. Consistently with these results, deficiency of phyB suppresses the elevated transcription of SUR2 in COL7 overexpression plants grown in high R:FR. Taking these results together with data suggesting that photo-excited phyB is required for stabilization of the COL7 protein, we argue that COL7 is a critical factor linking light perception to changes in auxin level in Arabidopsis.

Arabidopsis cryptochrome 2 (CRY2) is a blue-light receptor mediating blue-light inhibition of hypocotyl elongation and photoperiodic promotion of floral initiation. CRY2 is a constitutive nuclear protein that undergoes blue-light-dependent phosphorylation, ubiquitination, photobody formation, and degradation in the nucleus, but the relationship between these blue-light-dependent events remains unclear. It has been proposed that CRY2 phosphorylation triggers a conformational change responsible for the subsequent ubiquitination and photobody formation, leading to CRY2 function and/or degradation. We tested this hypothesis by a structure-function study, using mutant CRY2-GFP fusion proteins expressed in transgenic Arabidopsis. We show that changes of lysine residues of the NLS (Nuclear Localization Signal) sequence of CRY2 to arginine residues partially impair the nuclear importation of the CRY2K541R and CRY2K554/5R mutant proteins, resulting in reduced phosphorylation, physiological activities, and degradation in response to blue light. In contrast to the wild-type CRY2 protein that forms photobodies exclusively in the nucleus, the CRY2K541R and CRY2K554/5R mutant proteins form protein bodies in both the nucleus and cytosol in response to blue light. These results suggest that photoexcited CRY2 molecules can aggregate to form photobody-like structure without the nucleus-dependent protein modifications or the association with the nuclear CRY2-interacting proteins. Taken together, the observation that CRY2 forms photobodies markedly faster than CRY2 phosphorylation in response to blue light, we hypothesize that the photoexcited cryptochromes form oligomers, preceding other biochemical changes of CRY2, to facilitate photobody formation, signal amplification, and propagation, as well as desensitization by degradation.

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