###### Abstract  
Few studies have reported on the flowering time mechanism of tropical maize under short-day conditions. Drought, another important factor that affects flowering time, has been reported to delay the silking date in tropical maize. However, due to the lack of genetic information related to flowering in maize, the mechanism by which drought delays flowering is unclear. To further understand this process, we analyzed drought-responsive genes using RNA sequencing and identified genes related to flowering time, including contigs from de novo assembly. The results revealed changes in the expression of flowering-time genes, including _INDETERMINATE1 (ID1), Heading date 3a (Hda3a), CONSTANS-like genes, and ZEA MAYS CENTRORADIALES8 (ZCN8)_, which are known to be crucial factors in flowering. In particular, _Hd3a_, _CON21_, and _ZCN8_, which have been reported to accelerate flowering under short-day conditions, were downregulated by drought stress. Changes in gene expression appear to play an important role in changes in flowering time under drought. These expression profiles will help to further understand the flowering-time genes of tropical maize and the delayed flowering time resulting from drought. tropical maize; RNA-seq; drought; flowering time +
Footnote †: journal: Medical  
hormones [11; 12], gene networks [13; 14; 15], and transcription factors [16; 17; 18; 19]. The results of previous studies have also suggested that the drought response system of maize differs between tissues and development stages [19; 20; 21; 22; 23]. In addition, several papers on the drought stress response during the flowering stage have identified genes using GWAS [24; 25; 26; 27], gene expression profiles [19; 20; 28; 29; 30], and several transcription factors [31; 32; 33; 34]. Many studies have revealed genes related to flowering time in rice and _Arabidopsis_, but relatively few flowering-time genes of maize are known. Several studies have attempted to identify the role of maize flowering-time genes using _Arabidopsis_. As a result, differences in flowering time pathways were identified between dicot and monocot plants and between short-day (SD) and long-day (LD) conditions. For example, in rice under SD conditions, the increased expression of _Heading date 3a (Hd3a)_ induced _Early heading date 1 (Ehd1)_, which promoted flowering time, but this mechanism was not activated in dicot plants [35; 36]. Similarly, _GIGANTEA (GI)_ delayed flowering time in rice, but it exerted the opposite effect in _Arabidopsis_[37; 38]. In addition, _Heading date 1 (Hd1)_ promoted flowering in SD but repressed it in LD [39; 40; 41]. Since the discovery of the maize gene _INDETERMINATE 1 (ID1)_[42], various genes related to flowering time have been identified. _ID1_ is a zinc-finger transcription factor and is known to promote flowering time [43]. Maize contains a large number of _ZEA CENTRORADIALIS (ZCN)_ family genes that have similar functions to those of _AtFT_ and _AtFTL_[44]. _ZmZCN8_ is highly similar to _AtFT1_ and interacts with _DELAYED FLOWERING1 (ZmDLF1)_, an FD-like bZIP protein. The expression of _ZmZCN8_ was increased in the reproductive stage of the tropical line under SD, but it was unchanged in temperate maize [31; 45]. _ZmCONZ1_, an ortholog of _AtCO_ and _OsHd1_, is also known to regulate flowering by affecting the expression of _ZCN8_[31; 46]. However, there is no evidence that explains how _ZmCONZ1_ activates _ZmZCN8_ expression in SD conditions, and thus, the mechanism remains unclear. The role of _Hd3a_ has been reported to induce flowering time only under SD conditions. Under SD conditions, the expression of _Hd3a_ induces _Ehd1_, which promotes flowering [36]. However, most studies are based on B73, which is a temperate inbred line grown in long-day conditions. There is relatively little information on the tropical maize line, although the genes involved in flowering time are known to differ depending on the day length [29; 34; 47; 48] and maize genotype [18; 49; 50].