Yellow lupine (Lupinus luteus L., Taper c.), a member of the legume family (Fabaceae L.), has an enormous practical importance. Its excessive flower and pod abscission represents an economic drawback, as proper flower and seed formation and development is crucial for the plant's productivity. Generative organ detachment takes place at the basis of the pedicels, within a specialized group of cells collectively known as the abscission zone (AZ). During plant growth these cells become competent to respond to specific signals that trigger separation and lead to the abolition of cell wall adhesion. Little is known about the molecular network controlling the yellow lupine organ abscission. The aim of our study was to establish the divergences and similarities in transcriptional networks in the pods, flowers and flower pedicels abscised or maintained on the plant, and to identify genes playing key roles in generative organ abscission in yellow lupine. Based on de novo transcriptome assembly, we identified 166,473 unigenes representing 219,514 assembled unique transcripts from flowers, flower pedicels and pods undergoing abscission and from control organs. Comparison of the cDNA libraries from dropped and control organs helped in identifying 1,343, 2,933 and 1,491 differentially expressed genes (DEGs) in the flowers, flower pedicels and pods, respectively. In DEG analyses, we focused on genes involved in phytohormonal regulation, cell wall functioning and metabolic pathways. Our results indicate that auxin, ethylene and gibberellins are some of the main factors engaged in generative organ abscission. Identified 28 DEGs common for all library comparisons are involved in cell wall functioning, protein metabolism, water homeostasis and stress response. Interestingly, among the common DEGs we also found an miR169 precursor, which is the first evidence of micro RNA engaged in abscission. A KEGG pathway enrichment analysis revealed that the identified DEGs were predominantly involved in carbohydrate and amino acid metabolism, but some other pathways were also targeted. This study represents the first comprehensive transcriptome-based characterization of organ abscission in L. luteus and provides a valuable data source not only for understanding the abscission signaling pathway in yellow lupine, but also for further research aimed at improving crop yields.

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The floral development in an important legume crop yellow lupine (Lupinus luteus L., Taper cv.) is often affected by the abscission of flowers leading to significant economic losses. Small non-coding RNAs (sncRNAs), which have a proven effect on almost all developmental processes in other plants, might be of key players in a complex net of molecular interactions regulating flower development and abscission. This study represents the first comprehensive sncRNA identification and analysis of small RNA, transcriptome and degradome sequencing data in lupine flowers to elucidate their role in the regulation of lupine generative development. As shedding in lupine primarily concerns flowers formed at the upper part of the inflorescence, we analyzed samples from extreme parts of raceme separately and conducted an additional analysis of pedicels from abscising and non-abscising flowers where abscission zone forms. A total of 394 known and 28 novel miRNAs and 316 phased siRNAs were identified. In flowers at different stages of development 59 miRNAs displayed differential expression (DE) and 46 DE miRNAs were found while comparing the upper and lower flowers. Identified tasiR-ARFs were DE in developing flowers and were strongly expressed in flower pedicels. The DEmiR-targeted genes were preferentially enriched in the functional categories related to carbohydrate metabolism and plant hormone transduction pathways. This study not only contributes to the current understanding of how lupine flowers develop or undergo abscission but also holds potential for research aimed at crop improvement.

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In this work we studied interactions between auxin and ethylene in the inhibition of photoperiodic flower induction in SDP Pharbitis nil. To this end, PnACS2 was cloned and its expression was studied under various photoperiodic conditions, as well as under the influence of auxin. The full-length PnACS2 cDNA consists of 1,841 bp and encodes for 472 amino acids, with the 80-bp 5 0 -and the 417-bp 3 0 -untranslated regions. It was shown that the gene is transcribed in all organs of 5-day-old seedlings and that it is strongly activated by auxin. The maximal transcriptional activity of PnACS2 and the strongest stimulation of its activity by IAA occur in the cotyledons. This confirms the speculation that the inhibitory effect of auxin on P. nil flowering results from its stimulatory effect on ethylene production.

Application of gibberellic acid (GA 3 ) on the cotyledons of 5-d-old Pharbitis nil reversed the inhibitory effect of both abscisic acid (ABA) and ethylene on flowering. Application of GA 3 slightly decreased ethylene production and did not affect the endogenous ABA content in the cotyledons during the night. However, it reversed the stimulating effect of ABA on ethylene production.

In this study, the first ACC oxidase (PnACO1) cDNA from model short-day plant Pharbitis nil was isolated. The expression pattern of PnACO1 was studied under different conditions (photoperiod and auxin), an adequate balance of which determines P. nil flowering. It was shown that the gene was transcribed in all the examined organs of the 5-day-old seedling and was strongly activated by auxin. Our results also revealed that PnACO1 transcript accumulation in the cotyledons showed diurnal oscillations under both LD and SD conditions. On the basis of presented and previously obtained data, we suggest that flowering inhibition evoked by IAA in P. nil results from its stimulatory effect on both ACC synthase and oxidase gene expression and, consequently, enhances ethylene production.