Small auxin upregulated RNA (SAUR) gene family in maize: identification, evolution, and its phylogenetic comparison with Arabidopsis, rice, and sorghum.

Small auxin-up RNAs (SAURs) are the early auxin-responsive genes represented by a large multigene family in plants. Here, we identified 79 SAUR gene family members from maize (Zea mays subsp. mays) by a reiterative database search and manual annotation. Phylogenetic analysis indicated that the SAUR proteins from Arabidopsis, rice, sorghum, and maize had divided into 16 groups. These genes were non-randomly distributed across the maize chromosomes, and segmental duplication and tandem duplication contributed to the expansion of the maize SAUR gene family. Synteny analysis established orthology relationships and functional linkages between SAUR genes in maize and sorghum genomes. We also found that the auxin-responsive elements were conserved in the upstream sequences of maize SAUR members. Selection analyses identified some significant site-specific constraints acted on most SAUR paralogs. Expression profiles based on microarray data have provided insights into the possible functional divergence among members of the SAUR gene family. Quantitative real-time PCR analysis indicated that some of the 10 randomly selected ZmSAUR genes could be induced at least in maize shoot or root tissue tested. The results reveal a comprehensive overview of the maize SAUR gene family and may pave the way for deciphering their function during plant development.