The fasciclin-like arabinogalactan protein (FLA) family is involved in important plant wall formation and mechanical strength of the stems, and has never been systematically characterized in soybean (Glycine max), a huge crop in which stem lodging has been the cause of significant losses in yield. Here, we found that the soybean genome has 64 GmFLA genes, or a considerable increase over Arabidopsis, rice, and poplar, and these genes were grouped into three phylogenetic clusters (A, B, and C) that have varied domain structures. Evolutionary studies showed that duplication of segments was the most common cause of family expansion, with all the duplicated pairs of genes undergoing robust purifying selection. Tissue-specific expression profiling revealed that about a third of GmFLA genes is specifically expressed in stems. In nine stem-preferential genes assayed in six soybean varieties with varying stem thickness, the five stem-thick (diameter > 11 mm) varieties had a consistently lower expression of the five genes, GmFLA62, GmFLA43, GmFLA50, GmFLA07, and GmFLA56, than the thick-stem. These results are the first genomic resource of the GmFLA gene family in soybean and also determine certain candidate genes, which are different with the stem thickness, an important determinant of lodging. The findings of this study reveal a novel relationship between FLA gene expression and stem architecture, and suggest both as prospective targets for genetic improvement of lodging resistance and yield stability in soybean.
Abdelraouf et al. (Thu,) studied this question.