Global Transcriptome Analysis Revealed the Molecular Regulation Mechanism of Pigment and Reactive Oxygen Species Metabolism During the Stigma Development of Carya cathayensis

The RING zinc finger protein LbRZF1 promotes salt gland development and salt tolerance in Limonium bicolor

The recretohalophyte Limonium bicolor thrives in high-salinity environments because salt glands on the above-ground parts of the plant help to expel excess salt. Here, we characterize a nucleus-localized C3HC4 (RING-HC)-type zinc finger protein of L. bicolor named  RING  ZINC  FINGER PROTEIN  1 (LbRZF1). LbRZF1 was expressed in salt glands and in response to NaCl treatment. LbRZF1 showed no E3 ubiquitin ligase activity. The phenotypes of overexpression and knockout lines for LbRZF1 indicated that LbRZF1 positively regulated salt gland development and salt tolerance in L. bicolor. lbrzf1 mutants had fewer salt glands and secreted less salt than did the wild-type, whereas LbRZF1-overexpressing lines had opposite phenotypes, in keeping with the overall salt tolerance of these plants. A yeast two-hybrid screen revealed that LbRZF1 interacted with LbCATALASE2 (LbCAT2) and the transcription factor LbMYB113, leading to their stabilization. Silencing of LbCAT2 or LbMYB113 decreased salt gland density and salt tolerance. The heterologous expression of LbRZF1 in Arabidopsis thaliana conferred salt tolerance to this non-halophyte. We also identified the transcription factor LbMYB48 as an upstream regulator of LbRZF1 transcription. The study of LbRZF1 in the regulation network of salt gland development also provides a good foundation for transforming crops and improving their salt resistance.

Characteristic analysis of BZR genes family and their responses to hormone treatments and abiotic stresses in Carya illinoinensis

As the core of Brassinosteroids (BR) signaling pathway, BR-resistant (BZR) transcription factor regulates thousands of targeted genes mediating photomophogenesis, pollen sterility, cell expansion and stress response. Pecan (Carya illinoinensis) is a famous trees species of Carya, and its nut has high nutritional and economic values. However, there has no report on BZR genes family in pecan yet. Herein, totals of seven CiBZR members were identified in pecan genome, which were predicted to be hydrophilic unstable proteins and located in the nucleus. CiBZR genes had close evolutionary relationships with CcBZRs and JrBZRs in both Carya cathayensis and Juglans regia. These seven CiBZR genes were located independently on 7 chromosomes without doubling or tandem duplication. Based on the analysis of conserved motifs and gene structures, CiBZR genes were divided into three categories. More than 40 cis-acting elements were found in the 2 kb promoter regions of CiBZRs, which were mainly involved in hormone, light, and stress response, and plant growth and development. Notably, some of these CiBZR proteins were mainly located in the nucleus, had the self-activation ability and interaction relationship with BIN2 kinase, and negatively regulated the expression of CiCPD and CiDWF4. Gene expressions analysis further showed that CiBZR genes could express in many tissues and shared similar expression trends during embryo development. Moreover, most CiBZR genes responded to BR, Gibberellin (GA), Strigolactone (SL), salt, acid and osmotic stress. This study provides theoretical basis for the subsequent study on the role of CiBZR family genes in plant growth, development and stress responses.

Analysis of Delta(9) fatty acid desaturase gene family and their role in oleic acid accumulation in Carya cathayensis kernel

Carya cathayensis, commonly referred to as Chinese hickory, produces nuts that contain high-quality edible oils, particularly oleic acid (18:1). It is known that stearoyl-ACP desaturase (SAD) is the first key step converting stearic acid (C18:0, SA) to oleic acid (C18:1, OA) in the aminolevulinic acid (ALA) biosynthetic pathway and play an important role in OA accumulation. Thus far, there is little information about SAD gene family in C. cathayensis and the role of individual members in OA accumulation. This study searched the Chinese Hickory Genome Database and identified five members of SAD genes, designated as CcSADs, at the whole genome level through the comparison with the homologous genes from Arabidopsis. RNA-Seq analysis showed that CcSSI2-1, CcSSI2-2, and CcSAD6 were highly expressed in kernels. The expression pattern of CcSADs was significantly correlated with fatty acid accumulation during the kernel development. In addition, five full-length cDNAs encoding SADs were isolated from the developing kernel of C. cathayensis. CcSADs-green fluorescent protein (GFP) fusion construct was infiltrated into tobacco epidermal cells, and results indicated their chloroplast localization. The catalytic function of these CcSADs was further analyzed by heterologous expression in Saccharomyces cerevisiae, Nicotiana benthamiana, and walnut. Functional analysis demonstrated that all CcSADs had fatty acid desaturase activity to catalyze oleic acid biosynthesis. Some members of CcSADs also have strong substrate specificity for 16:0-ACP to synthesize palmitoleic acid (C16:1, PA). Our study documented SAD gene family in C. cathayensis and the role of CcSSI2-1, CcSSI2-2, and CcSAD6 in OA accumulation, which could be important for future improvement of OA content in this species via genetic manipulation.

WRINKLED1 Positively Regulates Oil Biosynthesis in Carya cathayensis

Hickory (Carya cathayensis Sarg.) is a kind of important woody oil tree species, and its nut has high nutritional value. Previous gene coexpression analysis showed that WRINKLED1 (WRI1) may be a core regulator during embryo oil accumulation in hickory. However, its specific regulatory mechanism on hickory oil biosynthesis has not been investigated. Herein, two hickory orthologs of WRI1 (CcWRI1A and CcWRI1B) containing two AP2 domains with AW-box binding sites and three intrinsically disordered regions (IDRs) but lacking the PEST motif in the C-terminus were characterized. They are nucleus-located and have self-activated ability. The expression of these two genes was tissue-specific and relatively high in the developing embryo. Notably, CcWRI1A and CcWRI1B can restore the low oil content, shrinkage phenotype, composition of fatty acid, and expression of oil biosynthesis pathway genes of Arabidopsis wri1-1 mutant seeds. Additionally, CcWRI1A/B were shown to modulate the expression of some fatty acid biosynthesis genes in the transient expression system of nonseed tissues. Transcriptional activation analysis further indicated that CcWRI1s directly activated the expression of SUCROSE SYNTHASE2 (SUS2), PYRUVATE KINASE β SUBUNIT 1 (PKP-β1), and BIOTIN CARBOXYL CARRIER PROTEIN2 (BCCP2) involved in oil biosynthesis. These results suggest that CcWRI1s can promote oil synthesis by upregulating some late glycolysis- and fatty acid biosynthesis-related genes. This work reveals the positive function of CcWRI1s in oil accumulation and provides a potential target for improving plant oil by bioengineering technology.