Genome-wide identification and expression analysis of transcription factors in Solanum lycopersicum

Identification of CAMTA Gene Family in Heimia myrtifolia and Expression Analysis under Drought Stress

Calmodulin-binding transcription factor (CAMTA) is an important component of plant hormone signal transduction, development, and drought resistance. Based on previous transcriptome data, drought resistance genes of the Heimia myrtifolia CAMTA transcription factor family were predicted in this study. The physicochemical characteristics of amino acids, subcellular localization, transmembrane structure, GO enrichment, and expression patterns were also examined. The results revealed that H. myrtifolia has a total of ten members (HmCAMTA1~10). Phylogenetic tree analysis of the HmCAMTA gene family revealed four different branches. The amino acid composition of CAMTA from H. myrtifolia and Punica granatum was quite similar. In addition, qRT-PCR data showed that the expression levels of HmCAMTA1, HmCAMTA2, and HmCAMTA10 genes increased with the deepening of drought, and the peak values appeared in the T4 treatment. Therefore, it is speculated that the above four genes are involved in the response of H. myrtifolia to drought stress. Additionally, HmCAMTA gene expression was shown to be more abundant in roots and leaves than in other tissues according to tissue-specific expression patterns. This study can be used to learn more about the function of CAMTA family genes and the drought tolerance response mechanism in H. myrtifolia.

The SlWRKY81 transcription factor inhibits stomatal closure by attenuating nitric oxide accumulation in the guard cells of tomato under drought

The WRKY transcription factors (TFs) play multifaceted roles in plant growth, development, and stress response. Previously, we found that SlWRKY81 negatively regulates tomato tolerance to drought; however, the mechanisms of stomatal regulation in response to drought remain largely unclear. Here, we showed that drought-induced upregulation in the SlWRKY81 transcripts induced photoinhibition and reduced the net photosynthetic rate in tomato leaves. However, silencing SlWRKY81 alleviated those inhibitions and minimized the drought-induced damage. A time-course of water loss showed that SlWRKY81 silencing significantly and consistently reduced leaf water loss, suggesting a role for SlWRKY81 in stomatal movement. Further analysis using light microscopy revealed that SlWRKY81 silencing significantly decreased stomatal aperture and increased the ratio of length to width of stomata under drought. Both biochemical assay and confocal laser scanning microscopy demonstrated that drought-induced upregulation in SlWRKY81 expression inhibited the nitric oxide (NO) accumulation in the guard cells, which was attributed to the simultaneous declines in the activity of nitrate reductase (NR) and NR expression in tomato leaves. The inspection of 3-kb sequences upstream of the predicted transcriptional start site of the NR identified three copies of the core W-box (TTGACC/T) sequence in the promoter region, indicating possible targets of SlWRKY81. Taken together, these data suggest that SlWRKY81 potentially represses NR transcription and thus reduces NO accumulation to attenuate stomatal closure and subsequent drought tolerance. These findings provide an improved understanding of the mechanism of WRKY-induced regulation of stomatal closure, which can be exploited in the future to enhance drought tolerance in crops.

Identification and Expression Analysis of GRAS Transcription Factor Genes Involved in the Control of Arbuscular Mycorrhizal Development in Tomato

The formation and functioning of arbuscular mycorrhizal (AM) symbiosis are complex and tightly regulated processes. Transcriptional regulation mechanisms have been reported to mediate gene expression changes closely associated with arbuscule formation, where nutrients move between the plant and fungus. Numerous genes encoding transcription factors (TFs), with those belonging to the GRAS family being of particular importance, are induced upon mycorrhization. In this study, a screening for candidate transcription factor genes differentially regulated in AM tomato roots showed that more than 30% of known GRAS tomato genes are upregulated upon mycorrhization. Some AM-upregulated GRAS genes were identified as encoding for transcription factors which are putative orthologs of previously identified regulators of mycorrhization in other plant species. The symbiotic role played by other newly identified AM-upregulated GRAS genes remains unknown. Preliminary results on the involvement of tomato SlGRAS18, SlGRAS38, and SlGRAS43 from the SCL3, SCL32, and SCR clades, respectively, in mycorrhization are presented. All three showed high transcript levels in the late stages of mycorrhization, and the analysis of promoter activity demonstrated that SlGRAS18 and SlGRAS43 are significantly induced in cells containing arbuscules. When SlGRAS18 and SlGRAS38 genes were silenced using RNA interference in hairy root composite tomato plants, a delay in mycorrhizal infection was observed, while an increase in mycorrhizal colonization was observed in SlGRAS43 RNAi roots. The possible mode of action of these TFs during mycorrhization is discussed, with a particular emphasis on the potential involvement of the SHR/SCR/SCL3 module of GRAS TFs in the regulation of gibberellin signaling during mycorrhization, which is analogous to other plant developmental processes.