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Abstract Background Photoperiod is an important environmental cue interacting with circadian clock pathway to optimize the local adaption and yield of crops. Quinoa (Chenopodium quinoa) in family Amaranthaceae has been known as superfood due to the nutritious elements. As quinoa was originated from the low-latitude Andes, most of the quinoa accessions are short-day type. Short-day type quinoa usually displays altered growth and yield status when introduced into higher latitude regions. Thus, deciphering the photoperiodic regulation on circadian clock pathway will help breed adaptable and high yielding quinoa cultivars. Results In this study, we conducted RNA-seq analysis of the diurnally collected leaves of quinoa plants treated by short-day (SD) and long-day conditions (LD), respectively. We identified 19,818 (44% of global genes) rhythmic genes in quinoa using HAYSTACK analysis. We identified the putative circadian clock architecture and investigated the photoperiodic regulatory effects on the expression phase and amplitude of global rhythmic genes, core clock components and transcription factors. The global rhythmic transcripts were involved in time-of-day specific biological processes. A higher percentage of rhythmic genes had advanced phases and strengthened amplitudes when switched from LD to SD. The transcription factors of CO-like, DBB, EIL, ERF, NAC, TALE and WRKY families were sensitive to the day length changes. We speculated that those transcription factors may function as key mediators for the circadian clock output in quinoa. Besides, we identified 15 novel time-of-day specific motifs that may be key cis elements for rhythm-keeping in quinoa. Conclusions Collectively, this study lays a foundation for understanding the circadian clock pathway and provides useful molecular resources for adaptable elites breeding in quinoa.

Quinoa (Chenopodium quinoa) is a prospective orphan crop that needs yield improvement. Previous studies indicate PHOSPHATIDYLETHANOLAMINE BINDING PROTEIN (PEBP) family genes are highly associated with the key agronomic traits of crops. Characterizing the pivotal PEBP genes will speed up the domestication and yield improvement of quinoa. Previous investigations on PEBP genes of Chenopodium species indicated that, the PEBP genes, despite in the same subclade, may have experienced functional diversification. Especially, the allotetraploidy (AABB) and numerous segmental duplications and chromosomal rearrangements in quinoa make it more difficult to understand the functions of PEBP genes. More recently, 6 quinoa FT subfamily genes were predicted to be related to flowering of quinoa. However, investigation on the whole PEBP family members is still lacking. In this study, we obtained 23 PEBP genes, including 5 MFT, 11 FTL and 7 TFL genes. We found 7 orthologous gene pairs, from sub-genome A and sub-genome B, respectively, showing collinearities with sugar beet. Evolution analysis on PEBP genes of two quinoa sub-genomes, sugar beet and relatives of diploid ancestors indicated that, the reasons for gene duplication events varied and 4 tandem duplications are the major reason for PEBP family expansion. Tissue-specific expression analysis suggested that expression patterns are mostly differing between orthologous gene pairs. Analysis on gene expressions at 6 stages suggested the possible positive roles of CqFTL1/CqFTL2, CqFTL5, CqFTL8, CqFTL6/CqFTL9 and CqTFL6/CqTFL7, and negative roles of CqTFL1/CqTFL2/CqTFL3, CqTFL4/CqTFL5 in inflorescence branching. Expression analysis in ABA-treated seed, in combination with the cis-acting element distribution analysis, indicated that CqMFT2, CqMFT3 and CqMFT4 may regulate seed germination via ABA signaling. Observations on responses to night break and photoperiod changes highlighted the roles of CqFTL5 and CqFTL8 under short day, and CqFTL6 under long day for quinoa flowering. Further, co-expression network analysis indicated that 64 transcription factors may act upstream of CqFTL5 and CqFTL8 to regulate flowering. Together, this study will help us identify the pivotal PEBP genes that may be utilized for quinoa breeding in future.