Map-based Cloing And Functional Analysis On The Maize LAZY1Gene

The plant hormone auxin plays important role in multitude of physiological and developmental processes including shoot gravitropism and inflorescence development. Despite many genes have been characterized to be involved in either process, few regulators, if any, have been identified to mediate both gravitropism and inflorescence development in a given species. The classical maize mutant lazy plantl (laI) have been known for decades to have defected gravitropic response, yet the mechanism underlining maize gravitropism remain largely elusive.In this research, we combined genetic analyses, developmental techniques, biochemical tools with transcriptome analyses to identify LAI, an ortholog of LAZY1in rice and in Arabidopsis, regulating both shoot gravitropism and inflorescence development in maize. The major novel discoveries of our study are:1) We created a maize prostratel (psl) mutant from our MuDR mutant library, which is allelic to the classic lal mutant, displaying a prostrate phenotype with reduced shoot gravitropism. We map-based cloned the LAI gene. Unlike its orthologs in rice or Arabidopsis, maize LAI regulates maize inflorescence development, and consistently, LAI is highly expressed in the reproductive organs.2) Transcription of LAI is responsive to both auxin and light. Exogenous auxin treatment led to a repression-then-induction pattern for LAI expression, while dark dramatically induced the transcript accumulation of LAI and light inhibited it.3) LA1protein localizes to the plasma membrane as well as in the nucleus. LA1physically interacts with a putative auxin transport regulator (Protein Kinase C, PKC) in the plasma membrane and a putative auxin signaling protein (AUX/IAA protein IAA17) in the nucleus, linking LA1with auxin transport and auxin signaling.4) RNA-SEQ analyses of lal mutant node showed auxin transport related genes, such as ZmPIN1c, were greatly downregulated while maize BR2(ZmABCBl) was significantly upregulated, consistant with the bilateral function of LA1of suppressing the basipetal polar auxin transport (PAT) while promoting the lateral PAT in maize. Further, most auxin responsive elements and light signaling genes were differentially up-regulated in the lal nodes, implying that LA1may act as a negative regulator for both light signaling and auxin signaling.Taken together, our findings suggest that LA1may mediate the crosstalk between shoot gravitropism and inflorescence development by regulating auxin transport, auxin signaling and probably light response in maize. As such, the results not only advance our understanding of the function of LA1in response to gravity, but also give new insights into the complicated crosstalk between auxin, light and inflorescent development.