Photoperiod effects on guar (Cyamopsis tetragonoloba L.)

Guar (Cyamopsis tetragonoloba), a short-day annual legume plant, is an economically important industrial crop with richness in high valuable guar gum. The photoperiod limits guar’s cultivated region, however, the mechanism of photoperiod effects on guar remains ambiguous. Based on Illumina RNA-seq, PacBio Iso-seq and UPLC-MS for analysis, the current study used different photoperiods to cultivate guar to illustrate the mechanism. The results showed that numerous genes responded to photoperiods differentially, involved in rhythm, flowering, biosynthesis and metabolism pathways. As processing time increased, the number of differentially expressed genes (DEGs) increased from 2518 to 5708. The genes of rhythm, flowering and key transcription factors phyA, GI, ELF3, TOC1, NF-Y and GATA positively responded to short-day, Whereas PRR, FLC, SVP, COL16 and B3 responded negatively to short-day, but positively to long-day. Additionally, the long-day inhibited the expression of genes related to phytohormones metabolism, such as GA synthetic correlation genes GA20ox and GA3ox, and JA synthesis genes AOS and ACX. As a result, the levels of GA and JA reduced, indicating their essential regulatory function in guar flowering. Furthermore, the expressions of the galactomannan synthesis genes were not influenced by photoperiod. In short, the phyA, GI, ELF3, TOC1, NF-Y, GATA, GA20ox and GA3ox were selected as candidate genes for flowering-promotion, while the PRR, FLC, SVP, COL16 and B3 for flowering-repression. This study provides several vital candidate genes for further genetic improvement for obtaining insensitive guar to photoperiod.