Expression analysis of <i>PIN</i>-formed auxin efflux transporter genes in maize

The local auxin gradient has a decisive role in auxin signaling, auxin-mediated development and abiotic stress response. PINFORMED (PIN)-formed auxin efflux transporters are very important for determining the direction of auxin transport and maintaining a local auxin concentration gradient. In this study, all candidate <i>PIN</i> genes from the current maize genome sequence database were identified and categorized based on amino acid similarity. The expression pattern of these <i>PIN</i>s was analyzed in maize inbred line DH4866, which was selected from the progeny of 7922 and 478, and served as the female parent line of many hybrids in Shandong Denghai Seeds Co Ltd (China). Tissue-specific expression patterns indicated that they may have different roles in different stages of development, especially in the root system. Promoter motif analysis of four maize <i>PIN1</i> genes and their expression levels in response to NAA, low phosphate levels and PEG treatment indicated that <i>ZmPIN1a</i> and <i>ZmPIN1b</i> may contribute more than <i>ZmPIN1c</i> and <i>ZmPIN1d</i> to root growth regulation and abiotic stress response. Analysis of the <i>ZmPIN1a</i> and <i>ZmPIN1b</i> transgenic lines (in DH4866) indicated that they have different effects on root development and growth, with <i>ZmPIN1a</i> increasing the number of lateral roots and inhibiting their elongation to form a developed root system, while <i>ZmPIN1b</i> increases root biomass by promoting the growth of both lateral and seminal roots. These results indicated that maize <i>PIN1</i> genes function in coordination during maize development and in response to abiotic stress.