Genome-Wide Identification and Expression Analyses of the Abscisic Acid Receptor PYR/PYL Gene Family in Response to Fruit Development and Exogenous Abscisic Acid in Luffa (Luffa cylindrica L.)

The pyrabactin resistance 1-like (PYR/PYL) proteins are abscisic acid receptors that perform multiple functions in various plant growth and development processes. However, the PYR/PYL gene family in luffa (Luffa cylindrica L.) has not been well-explored. In this study, we analysed the effects of whole-genome member identification, endogenous soluble sugars (SS), soluble proteins (SP), abscisic acid (ABA), indole-3-acetic acid (IAA, auxin) and the gene expression pattern of PYR/PYL influenced by exogenous abscisic acid (ABA) during the fruit development of luffa through the use of physiological and biochemical analyses, bioinformatics, and RT-qPCR techniques. We conducted a comprehensive genome-wide identification and characterisation of the PYR/PYL gene family in luffa fruit development. Four LcPYR and 10 LcPYL genes were identified in the luffa reference genome via bioinformatics analyses. A chromosomal mapping of the identified LcPYR/PYL genes showed that they were distributed on 9 of the 13 chromosomes in the luffa genome. Conserved structural domain analyses of the 14 proteins encoded by the LcPYR/PYL genes identified the PYR_PYL_RCAR_like structural domains typical of this family; however, no regulatory component of abscisic acid receptor (RCAR)-type genes was found. At six luffa fruit development stages (i.e., 0, 3, 6, 9, 12, and 15 days after pollination), the contents of soluble sugars, soluble proteins, and endogenous hormones ABA and IAA in the fruit significantly increased. Under the exogenous ABA treatments, the contents of these four endogenous substances in the fruits were significantly higher than they were in the control group at the same time period, and ABA and IAA seemed to be synergistically involved in the luffa fruit-ripening process. An analysis of the luffa transcriptome data and real-time fluorescence quantitative PCR (RT-qPCR) experiments showed that multiple LcPYR/PYLs (e.g., LcPYL10 and LcPYR4) had differential expression levels in the seven different tissues and exogenous ABA-treated fruits that were analysed, suggesting their roles in ABA hormone-mediated ripening of luffa fruit. Together, the results provide basic information about the LcPYR/PYL family in L. cylindrica and their involvement in fruit development.