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The NAC transcription factor ClNAC68 positively regulates sugar content and seed development in watermelon by repressing ClINV and ClGH3.6.

ABSTRACT: NAC (NAM, ATAF1/2, and CUC2) transcription factors play important roles in fruit ripening and quality. The watermelon genome encodes 80 NAC genes, and 21 of these NAC genes are highly expressed in both the flesh and vascular tissues. Among these genes, ClNAC68 expression was significantly higher in flesh than in rind. However, the intrinsic regulatory mechanism of ClNAC68 in fruit ripening and quality is still unknown. In this study, we found that ClNAC68 is a transcriptional repressor and that the repression domain is located in the C-terminus. Knockout of ClNAC68 by the CRISPR-Cas9 system decreased the soluble solid content and sucrose accumulation in mutant flesh. Development was delayed, germination was inhibited, and the IAA content was significantly decreased in mutant seeds. Transcriptome analysis showed that the invertase gene ClINV was the only gene involved in sucrose metabolism that was upregulated in mutant flesh, and expression of the indole-3-acetic acid-amido synthetase gene ClGH3.6 in the IAA signaling pathway was also induced in mutant seeds. EMSA and dual-luciferase assays showed that ClNAC68 directly bound to the promoters of ClINV and ClGH3.6 to repress their expression. These results indicated that ClNAC68 positively regulated sugar and IAA accumulation by repressing ClINV and ClGH3.6. Our findings provide new insights into the regulatory mechanisms by which NAC transcription factors affect fruit quality and seed development.

SUBMITTER: Wang J

PROVIDER: S-EPMC8484586 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The NAC transcription factors play important roles in regulating plant growth, development, and senescence, and responding to biotic and abiotic stressors in plants. A novel coding sequence (1,059 bp) was cloned from hexaploid triticale in this study. The putative protein (352 amino acids) encoded by this sequence was over 95% similar to the amino acid sequence of a NAC protein from Aegilops tauschii (XP020161331), and it formed a clade with Ae. tauschii, durum wheat, and barley. The putative protein contained a conserved nature actomyosin (NAM) domain (129 consecutive amino acids) between the 20th and 148th amino acids at the N-terminus and three transcription activation regions at the C-terminus. The novel gene was identified as a triticale NAC gene localized in the nucleus and designated as TwNAC01 (GenBank accession MG736919). The expression levels of TwNAC01 were the highest in roots, followed by leaves and stems when triticale lines were exposed to drought, polyethylene glycol 6,000 (PEG6000), NaCl, cold, methyl jasmonate (MeJA), and abscisic acid (ABA). Transgenic Arabidopsis thaliana overexpressing TwNAC01 had significantly lower leaf water loss rates and longer roots than wild-type (WT) A. thaliana. Virus-induced silencing of the TwNAC01 gene in triticale delayed root development and decreased length of primary root. Under drought stress, leaves of TwNAC01-silenced triticale had higher levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2), but lower relative water content (RWC), net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate than the leaves of the WT. Gene overexpression and silencing experiments suggested that TwNAC01 improves plant stress tolerance by increasing root length, regulating the water content of plant leaves by reducing MDA and H2O2 content, and adjusting respiration rate. The results suggest that TwNAC01 is a novel NAC transcription factor gene that can be exploited for triticale and cereal improvement.

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The NAC transcription factor ClNAC68 positively regulates sugar content and seed development in watermelon by repressing ClINV and ClGH3.6.

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