The Effect of 1-MCP on the Expression of Carotenoid, Chlorophyll Degradation, and Ethylene Response Factors in ‘Qihong’ Kiwifruit

The development of yellow color is an important aspect of fruit quality in yellow fleshed kiwifruit during fruit ripening, and it has a large influence on consumer preference. The yellow color is determined by carotenoid accumulation and chlorophyll degradation and is likely affected by ethylene production. This study investigates the expression of carotenoid, chlorophyll degradation, and ethylene response factors in ‘Qihong’ fruit, which had reached the near ripening stage (firmness ≈ 20 N) and were either left untreated (controls) or treated with 0.5 μL L−1 of 1-MCP for 12 h. Both the accumulation of β-carotene (not lutein) and degradation of chlorophyll a and b increased in response to the 1-MCP treatment, resulting in more yellow colored flesh in the 1-MCP treated fruit with higher carotenoid and lower chlorophyll contents. 1-MCP up-regulated AcLCY-β, AcSGR1, and AcPAO2, but reduced the expression of AcCCD1. These four genes were correlated with the concentrations of β-carotene and the chlorophylls. The expression of three ethylene response factors, including Acc29730, Acc25620, and Acc23763 were delayed and down-regulated in 1-MCP treated fruit, showing the highest correlation with the expression of AcLCY-β, AcSGR1, AcPAO2, and AcCCD1. Dual-Luciferase assays showed that 1-MCP treatment not only eliminated the inhibition of Acc23763 on the promoters of both AcPAO2 and AcLCY-β, but also reduced the activation of Acc29730 and Acc25620 on the AcCCD1 promoter. Our findings indicate that Acc29730, Acc25620, and Acc23763 may play an important role in the response to 1-MCP treatment during the fruit eating ripe stage, which likely altered the promoter activities of carotenoid and chlorophyll-related genes (AcPAO2, AcLCY-β and AcCCD1) to regulate their transcripts, resulting in more yellow color in the fruit flesh of ‘Qihong’.

Expression of an Antiviral Gene GmRUN1 from Soybean Is Regulated via Intron-Mediated Enhancement (IME)

Most of R (resistance) genes encode the protein containing NBS-LRR (nucleotide binding site and leucine-rich repeat) domains. Here, N. benthamiana plants were used for transient expression assays at 3–4 weeks of age. We identified a TNL (TIR-NBS-LRR) encoding gene GmRUN1 that was resistant to both soybean mosaic virus (SMV) and tobacco mosaic virus (TMV). Truncation analysis indicated the importance of all three canonical domains for GmRUN1-mediated antiviral activity. Promoter-GUS analysis showed that GmRUN1 expression is inducible by both salicylic acid (SA) and a transcription factor GmDREB3 via the cis-elements as-1 and ERE (ethylene response element), which are present in its promoter region. Interestingly, GmRUN1 gDNA (genomic DNA) shows higher viral resistance than its cDNA (complementary DNA), indicating the existence of intron-mediated enhancement (IME) for GmRUN1 regulation. We provided evidence that intron2 of GmRUN1 increased the mRNA level of native gene GmRUN1, a soybean antiviral gene SRC7 and also a reporter gene Luciferase, indicating the general transcriptional enhancement of intron2 in different genes. In summary, we identified an antiviral TNL type soybean gene GmRUN1, expression of which was regulated at different layers. The investigation of GmRUN1 gene regulatory network would help to explore the mechanism underlying soybean-SMV interactions.

AHK5 mediates ETR1-initiated multistep phosphorelay in Arabidopsis

Plants, like other sessile organisms, need to sense many different signals, and in response to them, modify their developmental programs to be able to survive in a highly changing environment. The multistep phosphorelay (MSP) in plants is a good candidate for a response mechanism that integrates multiple signal types both environmental and intrinsic in origin. Recently, ethylene was shown to control MSP activity via the histidine kinase (HK) activity of ETHYLENE RESPONSE 1 (ETR1)1,2, but the underlying molecular mechanism still remains unclear. Here we show that although ETR1 is an active HK, its receiver domain (ETR1RD) is structurally and functionally unable to accept the phosphate from the phosphorylated His in the ETR1 HK domain (ETR1HK) to initiate the phosphorelay to ARABIDOPSIS HISTIDINE-CONTAINING PHOSPHOTRANSMITTERs (AHPs), the next link downstream members in MSP signaling. Instead, ETR1 interacts with another HK ARABIDOPSIS HISTIDINE KINASE 5 (AHK5) and transfers the phosphate from ETR1HK through the receiver domain of AHK5 (AHK5RD), and subsequently to AHP1, AHP2 and AHP3, independently of the HK activity of AHK5. We show that AHK5 is necessary for ethylene-initiated, but not cytokinin-initiated, MSP signaling in planta and that it thus mediates hormonal control of root growth.

Genome-Wide Identification and Expression Analysis of AP2/EREBP Transcription Factors in Litchi (Litchi chinensis Sonn.)

APETALA2/ethylene response element binding proteins (AP2/EREBP) are a vital type of TF involved in plant organ development and embryogenesis. In this study we identified 202 Litchi AP2/EREBP TFs from the litchi genome. They were classified into four subfamilies by phylogenetic clustering, including AP2s (20), ERFs (112), DREBs (64), and RAVs (6). Analysis of conserved domains, motifs, gene structure, and genome localization were carried out to investigate the evolutionary features of litchi AP2/EREBPs. Over 35% of DREBs and ERFs involved in the expansion of litchi AP2/EREBPs resulted from tandem duplication. The majority of genomic organizations were conservative, except those of the AP2 subfamily, which had no intron and contained less conservative motif numbers. The expression profiles of litchi AP2/EREBPs in ten tissues were investigated using RNA-Seq data and fifty-nine showed tissue-specific expressions. Their expression patterns were confirmed by qRT-PCR with eight tissues-specificity genes. Six genes related to embryogenesis were identified using the map of orthologous gene interaction between Arabidopsis and litchi. This paper is a comprehensive report on the characteristics of the litchi AP2/EREBP gene superfamily. It will serve to further explore the regulatory mechanisms of AP2/EREBP TFs in the litchi somatic embryogenesis and provide information for litchi molecular breeding.

MPK3/MPK6-mediated ERF72 Phosphorylation Positively Regulates Resistance to Botrytis cinerea Through Directly and Indirectly Activating the Transcription of Camalexin-biosynthesis Enzymes

Ethylene response factor (ERF) Group VII members generally function in regulating plant growth and development, abiotic stress response, and plant immunity in Arabidopsis. However, the detail regulatory mechanism by which Group VII ERFs mediate plant immune responses remains elusive. Here, we characterised ERF72, a member of the Group VII ERFs, as a positive regulator mediating resistance to the necrotrophic pathogen Botrytis cinerea. Compared with wild type (WT), erf72 mutant showed the lower camalexin contents and more susceptible to B. cinerea, while complementation of ERF72 in erf72 rescued susceptibility phenotypes. Moreover, overexpression of ERF72 in WT promoted camalexin biosynthesis and resistance to B. cinerea. Then, we identified camalexin biosynthesis genes PAD3 and CYP71A13, and transcription factor WRKY33 as target genes of ERF72. Furthermore, MPK3 and MPK6 phosphorylate ERF72 at Ser151 to improve its transactivation activity, camalexin contents and resistance to B. cinerea. These findings highlight the role of ERF72 in coordinating the camalexin biosynthesis via directly regulating the expression of camalexin biosynthetic genes and indirectly by targeting WRKK33 in plant immunity.