Effects Of Brassinosteroid On Moso Bamboo Growth And Development And Its Regulation Mechanism Study

Moso bamboo(Phyllostachys edulis)is the the largest and most widely distributed economic bamboo species in China,which belongs to the genus of Phyllostachys in the Gramineae.Moso bamboo contains huge economic benefits and unique fast-growing patterns,whose shoot has the ability to elongate 1 meter per day at maximum.Recent research revealed that phytohormones are play important roles in the bamboo fast-growing processes.Brassinosteroids(BRs),as a kind of important plant steroids,plays an important role in promoting various plant development processes,such as cell elongation,cell differentiation,vascular development,fertility and response to biotic stress and abiotic stress.However,how brassinosteroid regulates moso bamboo seedlings or fast-growing shoot elongation remain unclear.In this study,the exogenous brassinolide and its synthesis inhibitor(propiconazole,PPZ)were applied to observe the BR’s effects on seedling and bamboo shoot growth.In addition,the transcriptome analysis was performed to identify BR responsive genes in moso bamboo shoot and root tissues.Furthermore,several BR responsive genes were cloned and transformed to Arabidopsis,which is helpful to further understand the mechanism how brassinosteroid regulates bamboo growth and development.Our main results are listed as follows:(1)We used 100 μM PPZ and 1 μM 2,4-epicastasterone(EBL)to treat the elongating bamboo shoots.After two days,EBL treatment promoted the elongation and bending of scale leaves,while PPZ inhibited the growth of scale leaves,and this growth repression could be restored by additional EBL treatment.These results show that BR is essential for the growth and development in the elongating moso bamboo shoot.(2)In order to uncover the role of BR in the growth of moso bamboo seedlings,PPZ and BR was applied to the 10-days old seedlings.Compared with the mock group,the moso bamboo height,root length and internode length were significantly decreased under 50 μM and 100 μM concentration PPZ treatment.Furthermore,PPZ treatment significantly reduced the leaf angle,while exogenous brassinolide treatment restored this phenotype in a dose-dependent manner.These results showed that BR are essential for bamboo growth and development in the seedling stage.(3)To further understand how BR works in moso bamboo,RNA-seq analysis was carried out on the shoots and roots of PPZ or BL treated seedlings respectively.The clustering of the change genes in PPZ treatment mainly focused on "cell wall organization or biogenesis","cellular response to the stress of plant oxidative","hydrogen peroxide catabolic process" and "phenylpropanoid metabolic process",while the genes affected by BR treatment were also concentrated in the clustering of "cell wall organization or biogenesis" and "hydrogen peroxide catabolic process".These indicated that BR plays a key role in cell wall development and cellular oxidation response in moso bamboo.(4)Three transcription factors that mediate auxin-dependent transcriptional regulation,AUXIN RESPONSE FACTORs(Pe ARFs)and thirteen ARF-interacting negative regulators,AUX/IAA(Pe IAAs)genes,were found as PPZ response genes.Interestingly,all Pe ARFs genes were up regulated and all Pe IAAs genes were down-regulated by PPZ treatment.When compared with the previous studies on moso bamboo IAA responsive genes,we found that 48.6% of the genes(67/138)responding to both BR and PPZ were affected by auxin.These results showed that there were complex interactions between BR and auxin pathway during the growth of moso bamboo.(5)By bioinformatics analysis,BBRGs(Bamboo BR regulate genes)which has no functional reports were selected out for further studies.These genes were cloned and overexpressed into Arabidopsis.Among 22 genes,BBRG14 gene encodes a mitochondria localized protein,which showing tissue-specific expression pattern in the elongating bamboo shoot.Over-expressing seedlings showed growth defects of cell elongation,quiescent center(QC)maintain and meristem zone in root apex in Arabidopsis.By studying the functions of BBRG14,we provide more scientific basis for revealing the molecular regulatory mechanism of BR in the growth and development of moso bamboo.