Long non-coding RNA transcriptome landscape of anthers at different developmental stages in response to drought stress in tomato.

Pollen development is particularly susceptible to drought stress. Long non-coding RNAs (lncRNAs) are known to play a role in plant development and responses to drought stress. However, the expression profile and putative function of lncRNAs in drought-induced male sterility remain largely unknown. In this study, we investigated the lncRNA transcriptome landscape of tomato anthers at early and late stages-tetrad-vacuolated microspore (TED-VUM) and binucleate-mature pollen (BIN-MP) anthers, respectively-in response to drought stress using RNA-sequencing. In total, we identified 67,770 lncRNAs, of which 3053 lncRNAs were drought responsive. Interestingly, there were more differentially expressed (DE) lncRNAs in TED-VUM (2879) than in BIN-MP (174) anthers, which was consistent with the TED-VUM anthers being more drought sensitive. Functional enrichment analysis revealed that the target genes of DE lncRNAs were significantly enriched in diverse metabolic processes, including in carbohydrate metabolism and hormone synthesis. Co-expression analysis also identified 1407 lncRNAs that strongly co-expressed with 8 target genes that are involved in hormone (abscisic acid and jasmonic acid) and carbohydrate (sucrose and starch) metabolisms and tapetum development, highlighting the potential of lncRNA-target-gene modulation of anther development under drought stress. Our results serve as a baseline for future investigations of the potential function of lncRNAs in plant reproductive development under drought stress.

Mitogen-activated protein kinase 4 is obligatory for late pollen and early fruit development in tomato.

Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules regulating vegetative and reproductive development of plants. However, the molecular mechanisms of the SlMPK4 gene in tomato pollen and fruit development remain elusive. SlMPK4 is preferentially and highly expressed in tomato stamens and its mRNA levels increase during early flower development, peaking at the mature pollen stage. Either up- or downregulation of SlMPK4 expression had no significant effect on tomato vegetative growth. However, RNAi-mediated suppression of SlMPK4 caused defects in pollen development, resulting in pollen abortion. The aborted pollen grains were either malformed or collapsed and completely lacked viability, resulting in a predominantly reduced fruit set rate in RNAi lines compared with control and overexpressing transgenic plants. Interestingly, seed development was inhibited in RNAi lines. Moreover, >12% of emasculated RNAi flowers developed seedless fruits without pollination. Anthers can produce typical microspore mother cells as well as uninucleate microspores, according to cytological investigations, while binucleate pollen ceased to produce typical mature pollen. Pollen abortion was further confirmed by transmission electron microscopy analysis at the binucleate stage in RNAi plants. The exine layer in aberrant pollen had a normal structure, while the intine layer appeared thicker. Suppression of SlMPK4 affects the transcript level of genes related to cell wall formation and modification, cell signal transduction, and metabolic and biosynthetic processes. A subset of genes that may be putative substrates of plant MAPKs were also differentially changed in RNAi transgenic flowers. Taken together, these results suggest that SlMPK4 plays a critical role in regulating pollen development and fruit development in tomato plants.

The MADS-Box Gene CsSHP Participates in Fruit Maturation and Floral Organ Development in Cucumber.

Cucumber is an important vegetable crop bearing fleshy pepo fruit harvested immature. Fruits left unpicked in time during summer production, as well as unfavorable environmental conditions during post-harvest shelf, will cause cucumber fruits to turn yellow and ripen, and thus impair the market value. Identification of maturity-related genes is of great agricultural and economic importance for cucumber production. Here, we isolated and characterized a MADS-box gene, Cucumis sativus SHATTERPROOF (CsSHP) in cucumber. Expression analysis indicated that CsSHP was specifically enriched in reproductive organs including stamens and carpels. Ectopic expression of CsSHP was unable to rescue the indehiscence silique phenotype of shp1 shp2 mutant plant in Arabidopsis. Instead, overexpression of CsSHP resulted in early flowering, precocious phenotypes, and capelloid organs in wild-type Arabidopsis. Biochemical analysis indicated that CsSHP directly interacted with cucumber SEPALLATA (SEP) proteins. CsSHP expression increased significantly during the yellowing stage of cucumber ripening, and was induced by exogenous application of abscisic acid (ABA). Therefore, CsSHP may participate in fruit maturation through the ABA pathway and floral organ specification via interaction with CsSEPs to form protein complex in cucumber.