Fig. 5

A cross-species comparison of the regulatory circuits controlling flowering and elongation in SAR between Arabidopsis and maize. a In Arabidopsis, the FKF1-GI module positively regulates the CO/FT module activity and flowering by multiple mechanisms. The FKF1/GI complex directly promotes CO expression on the CO promoter. FKF1 also directly enhances CO protein stability, or suppresses CDF transcription factors (mostly CDF1) to alleviate their repressive effect on CO expression. Moreover, GI was reported to directly promote FT expression. The Arabidopsis GI was reported to be a shade-inducible gene. In maize shade response, however, up-regulation of FKF1 in addition to GI and also the down-regulation of two CDFs were observed. b A recently revised model of auxin biosynthesis placed YUCCAs downstream of TAA1, with YUCCAs as the rate-limiting enzymes. In Arabidopsis, shade leads to strong induction of YUCCAs and a slight down-regulation of TAA1, resulting in excessive biosynthesis of auxin and elongated growth under shade. In maize, however, only a mild up-regulation of TAA1 and no obvious alterations in YUCCA expression were observed