Small Auxin Up RNA genes (SAURs) are early auxin-responsive genes, but whether any of them are involved in leaf senescence is not known. Auxin, on the other hand, has been shown to have a role in leaf senescence. Some of the external application experiments indicated that auxin can inhibit leaf senescence, whereas other experiments indicated that auxin can promote leaf senescence. Here, we report the identification and characterization of an Arabidopsis (Arabidopsis thaliana) leaf senescence-associated gene named SAG201, which is highly up-regulated during leaf senescence and can be induced by 1-naphthaleneacetic acid, a synthetic auxin. It encodes a functionally uncharacterized SAUR that has been annotated as SAUR36. Leaf senescence in transfer DNA insertion saur36 knockout lines was delayed as revealed by analyses of chlorophyll content, F_v/F_m ratio (a parameter for photosystem II activity), ion leakage, and the expression of leaf senescence marker genes. In contrast, transgenic Arabidopsis plants overexpressing SAUR36 (without its 3′ untranslated region [UTR]) displayed an early leaf senescence phenotype. However, plants overexpressing SAUR36 with its 3′ UTR were normal and did not exhibit the early-senescence phenotype. These data suggest that SAUR36 is a positive regulator of leaf senescence and may mediate auxin-induced leaf senescence and that the 3′ UTR containing a highly conserved downstream destabilizes the SAUR36 transcripts in young leaves.

Stevia (Stevia rebaudiana) is an important medicinal plant that yields diterpenoid steviol glycosides (SGs). SGs are currently used in the preparation of medicines, food products and neutraceuticals because of its sweetening property (zero calories and about 300 times sweeter than sugar). Recently, some progress has been made in understanding the biosynthesis of SGs in Stevia, but little is known about the molecular mechanisms underlying this process. Additionally, the genomics of Stevia, a non-model species, remains uncharacterized. The recent advent of RNA-Seq, a next generation sequencing technology, provides an opportunity to expand the identification of Stevia genes through in-depth transcript profiling. We present a comprehensive landscape of the transcriptome profiles of three genotypes of Stevia with divergent SG compositions characterized using RNA-seq. 191,590,282 high-quality reads were generated and then assembled into 171,837 transcripts with an average sequence length of 969 base pairs. A total of 80,160 unigenes were annotated, and 14,211 of the unique sequences were assigned to specific metabolic pathways by the Kyoto Encyclopedia of Genes and Genomes. Gene sequences of all enzymes known to be involved in SG synthesis were examined. A total of 143 UDP-glucosyltransferase (UGT) unigenes were identified, some of which might be involved in SG biosynthesis. The expression patterns of eight of these genes were further confirmed by RT-QPCR. RNA-seq analysis identified candidate genes encoding enzymes responsible for the biosynthesis of SGs in Stevia, a non-model plant without a reference genome. The transcriptome data from this study yielded new insights into the process of SG accumulation in Stevia. Our results demonstrate that RNA-Seq can be successfully used for gene identification and transcript profiling in a non-model species.

Three ω-3 fatty acid desaturase genes (CtFAD3, CtFAD7, and CtFAD8) were isolated from safflower (Carthamus tinctorius L.). Transcript analysis showed that the highest transcript levels were detected for CtFAD3 and the low transcript levels were detected for CtFAD7 and CtFAD8 in flowers. This result indicates that CtFAD3 enzyme activity is important for fatty acid desaturation in flowers. The low transcript level of CtFAD3 in developing seeds was consistent with the recorded high level of linoleic acid (18:2) and lack of linolenic acid (18:3) in safflower seed oil. At low temperatures, the induced transcription levels of ω-3 fatty acid desaturase genes in the stems and petioles were consistent with increased polyunsaturated fatty acids (PUFAs). In the roots, ω-3 fatty acid desaturase noticeably increased at low temperatures, whereas PUFA levels decreased. Interestingly, C18:3(Δ9,12,15) alcohol was specifically found in safflower roots, and showed a significant increase, indicating a flux in the acid to alcohol ratio of this compound in safflower roots.

The basic (region) leucine zippers (bZIPs) are evolutionarily conserved transcription factors widely distributed in eukaryotic organisms. In plants, they are not only involved in growth and development, defense and stress responses and regulation of physiological processes but also play a pivotal role in regulating secondary metabolism. To explore the function related to the bZIP gene family in Stevia rebaudiana Bertoni, we identified 105 SrbZIP genes at the genome-wide level and classified them into 12 subfamilies using bioinformation methods. Three main classes of cis-acting elements were found in the SrbZIP promoter regions, including development-related elements, defense and stress-responsive elements and phytohormone-responsive elements. Through protein–protein interaction network of 105 SrbZIP proteins, SrbZIP proteins were mainly classified into four major categories: ABF2/ABF4/ABI5 (SrbZIP51/SrbZIP38/SrbZIP7), involved in phytohormone signaling, GBF1/GBF3/GBF4 (SrbZIP29/SrbZIP63/SrbZIP60) involved in environmental signaling, AREB3 (SrbZIP88), PAN (SrbZIP12), TGA1 (SrbZIP69), TGA4 (SrbZIP82), TGA7 (SrbZIP31), TGA9 (SrbZIP95), TGA10 (SrbZIP79) and HY5 (SrbZIP96) involved in cryptochrome signaling, and FD (SrbZIP72) promoted flowering. The transcriptomic data showed that SrbZIP genes were differentially expressed in six S. rebaudiana cultivars (‘023’, ‘110’, ‘B1188’, ‘11-14’, ‘GP’ and ‘GX’). Moreover, the expression levels of selected 15 SrbZIP genes in response to light, abiotic stress (low temperature, salt and drought), phytohormones (methyl jasmonate, gibberellic acid and salicylic acid) treatment and in different tissues were analyzed utilizing qRT-PCR. Some SrbZIP genes were further identified to be highly induced by factors affecting glycoside synthesis. Among them, three SrbZIP genes (SrbZIP54, SrbZIP63 and SrbZIP32) were predicted to be related to stress-responsive terpenoid synthesis in S. rebaudiana. The protein–protein interaction network expanded the potential functions of SrbZIP genes. This study firstly provided the comprehensive genome-wide report of the SrbZIP gene family, laying a foundation for further research on the evolution, function and regulatory role of the bZIP gene family in terpenoid synthesis in S. rebaudiana.