Transcriptomic analysis demonstrates the early responses of local ethylene and redox signaling to low iron stress in Malus xiaojinensis

Malus xiaojinensis is an iron-efficient apple species, while the mechanism of its iron tolerance was not fully understood. This study was designed to obtain transcript sequence data and to examine gene expression in roots and leaves under iron deficiency based on RNA-Seq and bioinformatic analysis to provide a foundation for understanding the molecular mechanism of iron absorption after iron starvation. There were 74,839 transcripts with a mean length of 864 bp obtained from 454 and Illumina sequencing. The 21,037 transcripts were expressed differentially in root and leaf samples after iron starvation, involved in iron uptake, iron remobilization, and signal transduction based on GO biological process classification. Iron uptake was enhanced 12 h after iron deficiency treatment, while iron remobilization was reinforced after 2 days iron deficiency. Ethylene and reactive oxygen scavenger (ROS)-mediated signaling pathways were activated after 12 h of iron starvation, while the auxin-signaling pathway was inhibited at 12 h and activated on the 2nd day of iron starvation. Abscisic acid (ABA) and jasmonic acid (JA) signal pathway responded after 2 days of iron starvation. Therefore, in M. xiaojinensis, iron uptake was enhanced in the earlier period and iron remobilization was promoted in the later period of iron deficiency. Ethylene and ROS signaling pathway responded in the earlier period.