Objective This paper aims to identify the small auxin-up RNA (SAUR) family of auxin-responsive genes in Pinus tabuliformis, analyze its basic characteristics and role in drought stress, in order to provide a reference for the functional analysis of SAUR gene family in P. tabuliformis and other conifers.

Method Based on the whole genome data of P. tabuliformis, the SAUR gene family was identified by blast comparison. The gene structure, amino acid characteristics, chromosome localization, gene evolution, and gene function were analyzed using bioinformatics methods, and the expression patterns under drought stress were analyzed using RNA-Seq data. Result (1) A total of 66 SAUR family genes were identified in P. tabuliformis, named PtSAUR1−PtSAUR66. Among them, 60 SAUR family members were unevenly distributed on 9 chromosomes, mostly clustered. (2) The analysis of protein physicochemical characteristics showed that 76% of SAUR proteins were alkaline, and the subcellular prediction results showed that 74% of SAUR proteins can be localized in the nucleus. (3) The collinear relationship of SAUR genes of P. tabuliformis with Ginkgo biloba and Sequoiadendron giganteum showed that, compared with G. biloba, the homologous relationship between P. tabuliformis and S. giganteum was closer. (4) The prediction results of cis-acting elements showed that multiple hormones (methyl jasmonate, abscisic acid, auxin, etc.) and non-biological stress (low temperature, drought, etc.) related cis-acting elements were predicted in the promoters of the SAUR family genes. Among them, the number of elements related to methyl jasmonate was the highest, while the number of elements related to auxin was the lowest. (5) Systematic evolutionary analysis showed that the SAUR family proteins of P. tabuliformis can be divided into 7 groups. There were both SAUR proteins in P. tabuliformis, which was similar to angiosperms, as well as SAUR proteins unique to P. tabuliformis, which was previously isolated. (6) The RNA-Seq data analysis results showed that P. tabuliformis SAUR gene family had a certain regulatory effect on drought stress, with significant changes in the members of PtSAUR23, PtSAUR59, and PtSAUR66 genes, suggesting that they were key genes for drought resistance.

Conclusion The SAUR family genes of P. tabuliformis can participate in regulating drought stress, among which PtSAUR23, PtSAUR59, and PtSAUR66 may play a key role in this process.