MaNAC029 modulates ethylene biosynthesis and fruit quality and undergoes MaXB3-mediated proteasomal degradation during banana ripening. Journal of advanced research INTRODUCTIONS:Ethylene regulates ripening by activating various metabolic pathways that controlcolor, aroma, flavor, texture, and consequently, the quality of fruits. However, the modulation of ethylene biosynthesis and quality formation during banana fruit ripening remains unclear. OBJECTIVES:The present study aimed to identify the regulatory module that regulates ethylene and fruit quality-related metabolisms during banana fruit ripening. METHODS:We used RNA-seq to compare unripe and ripe banana fruits and identified a ripening-induced NAC transcription factor, MaNAC029. We further performed DNA affinity purification sequencing to identify the MaNAC029's target genes involved in ethylene biosynthesis and fruit quality formation, and electrophoretic mobility shift assay, chromatin immunoprecipitation with real-time polymerase chain reaction and dual luciferase assays to explore the underlying regulatory mechanisms. Immunoprecipitation combined with mass spectrometry, yeast two-hybrid assay, and bimolecular fluorescence complementation assay were used to screen and verify the proteins interacting with MaNAC029. Finally, the function of MaNAC029 and its interacting protein associated with ethylene biosynthesis and quality formation was verified through transient overexpression experiments in banana fruits. RESULTS:The study identified a nucleus-localized, ripening-induced NAC transcription factor MaNAC029. It transcriptionally activated genes associated with ethylene biosynthesis and a variety of cellular metabolisms related to fruit quality formation (cell wall degradation, starch degradation, aroma compound synthesis, and chlorophyll catabolism) by directly modulating their promoter activity during ripening. Overexpression of MaNAC029 in banana fruits activated ethylene biosynthesis and accelerated fruit ripening and quality formation. Notably, the E3 ligase MaXB3 interacted with and ubiquitinated MaNAC029 protein, facilitating MaNAC029 proteasomal degradation. Consistent with this finding, MaXB3 overexpression attenuated MaNAC029-enhanced ethylene biosynthesis and quality formation. CONCLUSION:Our findings demonstrate that a MaXB3-MaNAC029 module regulates ethylene biosynthesis and a series of cellular metabolisms related to fruit quality formation during banana ripening. These results expand the understanding of the transcriptional and post-translational mechanisms of fruit ripening and quality formation. 10.1016/j.jare.2022.12.004

Banana MKK1 modulates fruit ripening via the MKK1-MPK6-3/11-4-bZIP21 module. Cell reports The mitogen-activated protein kinase (MAPK) cascade consisting of MKKK, MKK, and MPK plays an indispensable role in various plant physiological processes. Previously, we showed that phosphorylation of MabZIP21 by MaMPK6-3 is involved in banana fruit ripening, but the regulatory mechanism by which MKK controls banana fruit ripening remains unclear. Here, ripening-induced MaMKK1 from banana fruit is characterized, and transiently overexpressing and silencing of MaMKK1 in banana fruit accelerates and inhibits fruit ripening, respectively, possibly by influencing phosphorylation and activity of MPK. MaMKK1 interacts with and phosphorylates MaMPK6-3 and MaMPK11-4 mainly at the pTEpY residues, resulting in MPK activation. MaMPK11-4 phosphorylates MabZIP21 to elevate its transcriptional activation ability. Transgenic tomato fruit expressing MabZIP21 ripen quickly with a concomitant increase in MabZIP21 phosphorylation. Additionally, MabZIP21 activates MaMPK11-4 and MaMKK1 transcription to form a regulatory feedback loop. Collectively, here we report a regulatory pathway of the MaMPK6-3/11-4-MabZIP21 module in controlling banana fruit ripening. 10.1016/j.celrep.2023.112832

Interaction of two MADS-box genes leads to growth phenotype divergence of all-flesh type of tomatoes. Nature communications All-flesh tomato cultivars are devoid of locular gel and exhibit enhanced firmness and improved postharvest storage. Here, we show that SlMBP3 is a master regulator of locular tissue in tomato fruit and that a deletion at the gene locus underpins the All-flesh trait. Intriguingly, All-flesh varieties lack the deleterious phenotypes reported previously for SlMBP3 under-expressing lines and which preclude any potential commercial use. We resolve the causal factor for this phenotypic divergence through the discovery of a natural mutation at the SlAGL11 locus, a close homolog of SlMBP3. Misexpressing SlMBP3 impairs locular gel formation through massive transcriptomic reprogramming at initial phases of fruit development. SlMBP3 influences locule gel formation by controlling cell cycle and cell expansion genes, indicating that important components of fruit softening are determined at early pre-ripening stages. Our findings define potential breeding targets for improved texture in tomato and possibly other fleshy fruits. 10.1038/s41467-021-27117-7

Expansin SlExp1 and endoglucanase SlCel2 synergistically promote fruit softening and cell wall disassembly in tomato. The Plant cell Fruit softening, an irreversible process that occurs during fruit ripening, can lead to losses and waste during postharvest transportation and storage. Cell wall disassembly is the main factor leading to loss of fruit firmness, and several ripening-associated cell wall genes have been targeted for genetic modification, particularly pectin modifiers. However, individual knockdown of most cell wall-related genes has had minimal influence on cell wall integrity and fruit firmness, with the notable exception of pectate lyase. Compared to pectin disassembly, studies of the cell wall matrix, the xyloglucan-cellulose framework, and underlying mechanisms during fruit softening are limited. Here, a tomato (Solanum lycopersicum) fruit ripening-associated α-expansin (SlExpansin1/SlExp1) and an endoglucanase (SlCellulase2/SlCel2), which function in the cell wall matrix, were knocked out individually and together using clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9-mediated genome editing. Simultaneous knockout of SlExp1 and SlCel2 enhanced fruit firmness, reduced depolymerization of homogalacturonan-type pectin and xyloglucan, and increased cell adhesion. In contrast, single knockouts of either SlExp1 or SlCel2 did not substantially change fruit firmness, while simultaneous overexpression of SlExp1 and SlCel2 promoted early fruit softening. Collectively, our results demonstrate that SlExp1 and SlCel2 synergistically regulate cell wall disassembly and fruit softening in tomato. 10.1093/plcell/koad291