Spatiotemporal regulation of JAZ4 expression and splicing contribute to ethylene- and auxin-mediated responses in Arabidopsis roots.

Jasmonic acid (JA) signaling controls several processes related to plant growth, development, and defense, which are modulated by the transcription regulator and receptor JASMONATE-ZIM DOMAIN (JAZ) proteins. We recently discovered that a member of the JAZ family, JAZ4, has a prominent function in canonical JA signaling as well as other mechanisms. Here, we discovered the existence of two naturally occurring splice variants (SVs) of JAZ4 in planta, JAZ4.1 and JAZ4.2, and employed biochemical and pharmacological approaches to determine protein stability and repression capability of these SVs within JA signaling. We then utilized quantitative and qualitative transcriptional studies to determine spatiotemporal expression and splicing patterns in vivo, which revealed developmental-, tissue-, and organ-specific regulation. Detailed phenotypic and expression analyses suggest a role of JAZ4 in ethylene (ET) and auxin signaling pathways differentially within the zones of root development in seedlings. These results support a model in which JAZ4 functions as a negative regulator of ET signaling and auxin signaling in root tissues above the apex. However, in the root apex JAZ4 functions as a positive regulator of auxin signaling possibly independently of ET. Collectively, our data provide insight into the complexity of spatiotemporal regulation of JAZ4 and how this impacts hormone signaling specificity and diversity in Arabidopsis roots.

JAZ4 is involved in plant defense, growth, and development in Arabidopsis.

Jasmonate zim-domain (JAZ) proteins comprise a family of transcriptional repressors that modulate jasmonate (JA) responses. JAZ proteins form a co-receptor complex with the F-box protein coronatine insensitive1 (COI1) that recognizes both jasmonoyl-l-isoleucine (JA-Ile) and the bacterial-produced phytotoxin coronatine (COR). Although several JAZ family members have been placed in this pathway, the role of JAZ4 in this model remains elusive. In this study, we observed that the jaz4-1 mutant of Arabidopsis is hyper-susceptible to Pseudomonas syringae pv. tomato (Pst) DC3000, while Arabidopsis lines overexpressing a JAZ4 protein lacking the Jas domain (JAZ4∆Jas) have enhanced resistance to this bacterium. Our results show that the Jas domain of JAZ4 is required for its physical interaction with COI1, MYC2 or MYC3, but not with the repressor complex adaptor protein NINJA. Furthermore, JAZ4 degradation is induced by COR in a proteasome- and Jas domain-dependent manner. Phenotypic evaluations revealed that expression of JAZ4∆Jas results in early flowering and increased length of root, hypocotyl, and petiole when compared with Col-0 and jaz4-1 plants, although JAZ4∆Jas lines remain sensitive to MeJA- and COR-induced root and hypocotyl growth inhibition. Additionally, jaz4-1 mutant plants have increased anthocyanin accumulation and late flowering compared with Col-0, while JAZ4∆Jas lines showed no alteration in anthocyanin production. These findings suggest that JAZ4 participates in the canonical JA signaling pathway leading to plant defense response in addition to COI1/MYC-independent functions in plant growth and development, supporting the notion that JAZ4-mediated signaling may have distinct branches.

Common bean reaction to angular leaf spot comprises transcriptional modulation of genes in the ALS10.1 QTL.

Genetic resistance of common bean (Phaseolus vulgaris L.) against angular leaf spot (ALS), caused by the fungus Pseudocercospora griseola, is conferred by quantitative trait loci (QTL). In this study, we determined the gene content of the major QTL ALS10.1 located at the end of chromosome Pv10, and identified those that are responsive to ALS infection in resistant (CAL 143) and susceptible (IAC-UNA) genotypes. Based on the current version of the common bean reference genome, the ALS10.1 core region contains 323 genes. Gene Ontology (GO) analysis of these coding sequences revealed the presence of genes involved in signal perception and transduction, programmed cell death (PCD), and defense responses. Two putative R gene clusters were found at ALS10.1 containing evolutionary related coding sequences. Among them, the Phvul.010G025700 was consistently up-regulated in the infected IAC-UNA suggesting its contribution to plant susceptibility to the fungus. We identified six other genes that were regulated during common bean response to P. griseola; three of them might be negative regulators of immunity as they showed opposite expression patterns during resistant and susceptible reactions at the initial phase of fungal infection. Taken together, these findings suggest that common bean reaction to P. griseola involves transcriptional modulation of defense genes in the ALS10.1 locus, contributing to resistance or susceptibility depending on the plant-pathogen interaction.