Characterization of the FLA Gene Family in Tomato (Solanum lycopersicum L.) and the Expression Analysis of SlFLAs in Response to Hormone and Abiotic Stresses

Genome-Wide Identification and Characterization of Tomato Fatty Acid β-Oxidase Family Genes KAT and MFP

Fatty acids and their derivatives play a variety of roles in living organisms. Fatty acids not only store energy but also comprise membrane lipids and act as signaling molecules. There are three main proteins involved in the fatty acid β-oxidation pathway in plant peroxisomes, including acyl-CoA oxidase (ACX), multifunctional protein (MFP), and 3-ketolipoyl-CoA thiolase (KAT). However, genome-scale analysis of KAT and MFP has not been systemically investigated in tomatoes. Here, we conducted a bioinformatics analysis of KAT and MFP genes in tomatoes. Their physicochemical properties, protein secondary structure, subcellular localization, gene structure, phylogeny, and collinearity were also analyzed. In addition, a conserved motif analysis, an evolutionary pressure selection analysis, a cis-acting element analysis, tissue expression profiling, and a qRT-PCR analysis were conducted within tomato KAT and MFP family members. There are five KAT and four MFP family members in tomatoes, which are randomly distributed on four chromosomes. By analyzing the conserved motifs of tomato KAT and MFP family members, we found that both KAT and MFP members are highly conserved. In addition, the results of the evolutionary pressure selection analysis indicate that the KAT and MFP family members have evolved mainly from purifying selection, which makes them more structurally stable. The results of the cis-acting element analysis show that SlKAT and SlMFP with respect may respond to light, hormones, and adversity stresses. The tissue expression analysis showed that KAT and MFP family members have important roles in regulating the development of floral organs as well as fruit ripening. The qRT-PCR analysis revealed that the expressions of SlKAT and SlMFP genes can be regulated by ABA, MeJA, darkness, NaCl, PEG, UV, cold, heat, and H2O2 treatments. These results provide a basis for the involvement of the SlKAT and SlMFP genes in tomato floral organ development and abiotic stress response, which lay a foundation for future functional study of SlKAT and SlMFP in tomatoes.

SlSERK3B Promotes Tomato Seedling Growth and Development by Regulating Photosynthetic Capacity

Brassinosteroids (BRs) are a group of polyhydroxylated steroids for plant growth and development, regulating numerous physiological and biochemical processes and participating in multi-pathway signaling in plants. 24-Epibrassinolide (EBR) is the most commonly used BR for the investigation of the effects of exogenous steroidal phytohormones on plant physiology. Although SlSERK3B is considered a gene involved in the brassinosteroid (BR) signaling pathway, its specific role in plant growth and development has not been reported in detail. In this study, tomato (Solanum lycopersicum L.) seedlings treated with 0.05 μmol L-1 EBR showed a significant increase in plant height, stem diameter, and fresh weight, demonstrating that BR promotes the growth of tomato seedlings. EBR treatment increased the expression of the BR receptor gene SlBRI1, the co-receptor gene SlSERK3A and its homologs SlSERK3B, and SlBZR1. The SlSERK3B gene was silenced by TRV-mediated virus-induced gene silencing (VIGS) technology. The results showed that both brassinolide (BL) content and BR synthesis genes were significantly up-regulated in TRV-SlSERK3B-infected seedlings compared to the control seedlings. In contrast, plant height, stem diameter, fresh weight, leaf area and total root length were significantly reduced in silenced plants. These results suggest that silencing SlSERK3B may affect BR synthesis and signaling, thereby affecting the growth of tomato seedlings. Furthermore, the photosynthetic capacity of TRV-SlSERK3B-infected tomato seedlings was reduced, accompanied by decreased photosynthetic pigment content chlorophyll fluorescence, and photosynthesis parameters. The expression levels of chlorophyll-degrading genes were significantly up-regulated, and carotenoid-synthesising genes were significantly down-regulated in TRV-SlSERK3B-infected seedlings. In conclusion, silencing of SlSERK3B inhibited BR signaling and reduced photosynthesis in tomato seedlings, and this correlation suggests that SlSERK3B may be related to BR signaling and photosynthesis enhancement.