Cell-specific clock-controlled gene expression program regulates rhythmic fiber cell growth in cotton

BackgroundThe epidermis of cotton ovule produces fibers, the most important natural cellulose source for the global textile industry. However, the molecular mechanism of fiber cell growth is still poorly understood.ResultsHere, we develop an optimized protoplasting method, and integrate single-cell RNA sequencing (scRNA-seq) and single-cell ATAC sequencing (scATAC-seq) to systematically characterize the cells of the outer integument of ovules from wild type and fuzzless/lintless (fl) cotton (Gossypium hirsutum). By jointly analyzing the scRNA-seq data from wildtype and fl, we identify five cell populations including the fiber cell type and construct the development trajectory for fiber lineage cells. Interestingly, by time-course diurnal transcriptomic analysis, we demonstrate that the primary growth of fiber cells is a highly regulated circadian rhythmic process. Moreover, we identify a small peptide GhRALF1 that circadian rhythmically controls fiber growth possibly through oscillating auxin signaling and proton pump activity in the plasma membrane. Combining with scATAC-seq, we further identify two cardinal cis-regulatory elements (CREs, TCP motif, and TCP-like motif) which are bound by the trans factors GhTCP14s to modulate the circadian rhythmic metabolism of mitochondria and protein translation through regulating approximately one third of genes that are highly expressed in fiber cells.ConclusionsWe uncover a fiber-specific circadian clock-controlled gene expression program in regulating fiber growth. This study unprecedentedly reveals a new route to improve fiber traits by engineering the circadian clock of fiber cells.

Automated summary

By combining single-cell RNA sequencing and single-cell ATAC sequencing, this study systematically characterizes the cells of cotton ovule integument and uncovers the molecular mechanism and circadian rhythmic regulation of fiber cell growth. The circadian clock-controlled gene expression program and a peptide GhRALF1 are identified to regulate fiber growth. The study also identifies cardinal cis-regulatory elements and their corresponding trans factors that modulate the circadian rhythmic metabolism and protein translation in fiber cells.