Genome-wide identification of CYP90family and functional analysis of NnCYP90B1 on rhizome enlargement in lotus

The CYP90 family is a crucial group of enzymes involved in the structural modification of brassinosteroids (BRs) and plays a pivotal role in regulating plant growth and development. However, information regarding the CYP90 family in lotus remains limited. Here, five members of the CYP90 family were identified in the lotus genome, distributed across four chromosomes. Analysis of exon/intron arrangements revealed that all NnCYP90 genes contained eight exons. Furthermore, all NnCYP90 proteins were found to be located within the endoplasmic reticulum and contained a typical heme-binding region. The promoter regions of NnCYP90 harbor numerous cis-acting elements associated with responses to light signals, hormone signals, plant growth, and development, as well as abiotic and biotic stress. The members of the NnCYP90 family were expressed in at least one tissue, with three genes in the NnCYP90B and NnCYP90D subfamilies exhibiting specific expression in underground tissues. NnCYP90B1, identified as a key rate-limiting enzyme in the BR synthesis pathway, displayed high expression levels in the rhizome of the temperate ecotype 'ZO', whereas its expression in the rhizome of the tropical ecotype 'DH' was comparatively low. Moreover, NnCYP90B1 expression was higher in the rhizome at the swelling stage than at the stolon stage. Overexpression of NnCYP90B1 in Solanum tuberosum resulted in early tuberization and increased tuber yield. Taken together, this study elucidates the genetic characteristics of the lotus CYP90 family genes and provides insights into the role of NnCYP90B1 in lotus rhizome development. These findings shed new light on the mechanisms underlying lotus rhizome enlargement.