The correlation between heavy metal chelation and transcriptional potential of GRAS genes in Broussonetia papyrifera

In order to understand the adaptation mechanism of Broussonetia papyrifera to heavy metal stress and then promote its remediation and utilization, in this study, a total of 24 GRAS transcription factors were identified from B. papyrifera transcriptomes. Their complete ORFs were 597–2250 bp in length with encoding proteins 22.40–84.13 kDa. The 24 BpGRASs were distributed across nine chromosomes and two scaffolds. Their promoters contained numerous cis-acting elements involving in plant development, environmental stimuli, and hormonal regulation. These BpGRAS genes were predominantly transcribed in flowers and fruits. The most prominent genes were BpSCL21b and BpDELLA1, whose expression levels in flowers were 4.11- and 4.56-fold higher than the minimal one in leaves. All BpGRASs were apparently induced by ABA and at least one treatment of Cd, Cu, Mn, and Zn. The expression of some BpGRAS genes (including BpSCL1d, BpSCL7, BpSCL27, BpSCL34, etc.) was significantly correlated with HM chelation and the non-protein thiols (NPT) accumulation, which was regarded as barriers to resist HM stress, under Cd, Cu, Mn, and Zn stress. Moreover, BpSCL15 and BpSCL21b transgenic yeast displayed significantly enhanced growth and viability (1.23-–2.71-fold, 1.30-–1.96-fold of control OD₆₀₀, accordingly) and metal accumulation (1.81-–3.58-fold, 1.91-–3.17-fold of control, accordingly). These results suggested that BpGRASs, especial BpSCL15, BpSCL21b, and BpSCL34, are essential for B. papyrifera response to HM stress depending on ABA signaling. It’s the first time to investigate the correlation of BpGRASs’ expression with HM and NPT accumulation, which may benefit for revealing the HM adaptation mechanism of B. papyrifera and provide candidate genes for HM resistance breeding in woody plants.