BZR1 Family Transcription Factors Function Redundantly and Indispensably in BR Signaling but Exhibit BRI1-Independent Function in Regulating Anther Development in Arabidopsis

Roles of Brassinosteroids in Plant Reproduction

“…While, AG expression is unaffected and SPL transcription is only reduced to about half in bri1-t [104]. Meanwhile, transcription of tapetal development genes like DYSFUNCTIONAL TAPETUM1 (DYT1) and ARABIDOPSIS THALIANA ANTHER 7 (ATA7) is largely diminished in the quintuple mutant [104,106,107]. In summary, BZR1 and its five homologs regulate the early stage of anther development through activating the expression of AG and SPL as well as tapetal development genes in both BR-dependent and independent manners.…”

“…However, by using the loss-of-function quintuple and hextuple mutants of BZR1 family members, it is found that BR downstream transcription factors regulate anther development in both BRI1-dependent and -independent ways [102,104]. Qunituple mutant of bes1-1 bzr1-1 beh1-1 beh3-1 beh4-1 is phenotypically like wild type but male-sterile and the hextuple mutants of all the six family members are phenotypically similar to the BR insensitive bri1 brl1 brl3 (bri1-t) in both vegetative and reproductive defects [102,104,105]. The anthers of the hextuples are failed to open with no pollen grains.…”

“…In anther development stage 1, only the L1 layer are developed in bzr-h, compared with clearly visible three layers of L1, L2 and L3 in both wild type and bri1-t. In stage 2, anther cells of bzr-h become severely vacuolated and archesporial cell formation is inhibited in stage 3, which causes the loculeless anther of bzr-h [104]. The sporogenesis and archesporial cell initiation are directly regulated by AG and SPL during early male gametogenesis and the expression of the AG and SPL is almost inhibited in bzr-h unopened flowers [59,63,104].…”

“…In stage 2, anther cells of bzr-h become severely vacuolated and archesporial cell formation is inhibited in stage 3, which causes the loculeless anther of bzr-h [104]. The sporogenesis and archesporial cell initiation are directly regulated by AG and SPL during early male gametogenesis and the expression of the AG and SPL is almost inhibited in bzr-h unopened flowers [59,63,104]. While, AG expression is unaffected and SPL transcription is only reduced to about half in bri1-t [104].…”

“…The sporogenesis and archesporial cell initiation are directly regulated by AG and SPL during early male gametogenesis and the expression of the AG and SPL is almost inhibited in bzr-h unopened flowers [59,63,104]. While, AG expression is unaffected and SPL transcription is only reduced to about half in bri1-t [104]. Meanwhile, transcription of tapetal development genes like DYSFUNCTIONAL TAPETUM1 (DYT1) and ARABIDOPSIS THALIANA ANTHER 7 (ATA7) is largely diminished in the quintuple mutant [104,106,107].…”